Women's health and female fertility: current evidence and knowledge gaps in the Asia-Pacific region.

Diet and nutrition are key modifiable risk factors for overall health, through their effects on multiple pathways such as obesity, oxidative stress, inflammation, and insulin resistance, all of which have been linked to fertility outcomes. 6 While research is still limited, significant progress has been made in recent decades in examining the associations between diet at various levels (i.e. dietary patterns, foods/food groups, and nutrients) and female fertility, both in the general population and among individuals undergoing fertility treatments. Several examples are highlighted below. Dietary patterns assess overall intake while accounting for foods and nutrient interactions. They help reflect real-world eating habits and inform public health recommendations. Several dietary patterns have been studied with female fertility. The Mediterranean diet (MD) , known for its health benefits, emphasises high intakes of fruits, vegetables, whole grains, legumes, and healthy fats (particularly olive oil and nuts), moderate consumption of dairy, fish, and wine, and limited red and processed meats. Research on the MD and fertility has been predominantly conducted in White populations. 6 In the general population, limited evidence indicates that greater adherence to the MD is associated with a lower risk of difficulty in conceiving but has no influence on pregnancy loss. 7 In women undergoing fertility treatments, a meta-analysis 6 of six fertility cohorts found no overall association with implantation, clinical pregnancy, or live birth, although specific studies showed significant associations with clinical pregnancy and live birth. Additionally, greater adherence to the MD was linked to a lower risk of pregnancy loss among those who conceived through fertility treatments. 8 Limited evidence from the Asia–Pacific population, for example, a fertility study conducted in China, did not observe significant associations between the MD and clinical fertility outcomes. 9 Overall, while the MD shows potential benefits for female fertility, the evidence remains inconsistent across populations and study settings, highlighting the need for further research in more diverse cohorts. The ‘ fertility diet ’ emphasises higher intakes of monounsaturated fats over trans fats, plant-based over animal proteins, low-glycaemic carbohydrates, high-fat dairy, multivitamins, and iron. 10 A modified version, the ‘pro-fertility diet’, prioritises folic acid, vitamin B12, vitamin D, low-pesticide fruits and vegetables, whole grains, seafood, dairy, and soy. 11 These diets have been linked to lower risks of infertility and pregnancy loss in women trying to conceive 10 and improved assisted reproductive technology (ART) outcomes. 11 Unlike the MD, the additional benefits of fertility/pro-fertility diets may come from vitamin supplements and reduced pesticide exposure. 11 These dietary patterns have been mainly studied in U.S. fertility cohorts, and further research is needed to assess their applicability in other populations. Folate is essential for cell growth and DNA synthesis and repair, making it a key micronutrient for reproductive health. A deficiency can lead to neural tube defects (NTDs). The World Health Organization (WHO) recommends 400 μg/day of folic acid supplementation from preconception through the first 12 weeks of gestation. 12 Evidence on folate's impact on female fertility and birth rates primarily comes from studies conducted in North America and Europe with mixed findings, though potential benefits are possible. Some randomised controlled trials (RCTs) and observational studies suggest that folate supplementation may improve fecundability, as well as pregnancy and birth rates, both in the general population and among those undergoing fertility treatments; however, null results have also been observed, likely due to differences in study design. 13 , 14 , 15 Beyond supplementation, greater dietary folate has been associated with improved fertility outcomes. 16 Adequate folate intake from supplements and folate-rich foods (leafy greens, beans, nuts, fortified foods) may support fertility and pregnancy health. Research on folate intake across diverse ethnic groups remains limited and warrants further investigation. Vitamin D receptors are widely expressed in female reproductive organs, and animal studies suggest that deficiency may impair reproduction. Globally, an estimated one billion people are affected by vitamin D deficiency (serum 25(OH)D < 20 ng/mL), 17 with higher prevalence in the Asia–Pacific region. 18 Women are generally more affected than men. Vitamin D can be obtained through sun exposure, certain foods (e.g., fatty fish, liver, egg yolks), and supplements. Most studies on vitamin D and fertility come from the U.S. and findings remain inconsistent. While some studies show vitamin D sufficiency, compared to insufficiency/deficiency, is associated with improved fecundability, higher pregnancy and live birth rates, and reduced pregnancy loss, 19 , 20 others find no such association. For instance, a cohort of preconception couples in China, in which 86.5% of female participants had vitamin D insufficiency, found no association between women's vitamin D insufficiency and pregnancy rates or time to pregnancy. 21 In ART, observational studies generally indicate improved pregnancy and birth rates with vitamin D sufficiency, 22 although short-term RCTs have not demonstrated significant effects of vitamin D supplementation on fertility outcomes. 15 While vitamin D deficiency may negatively impact fertility, further research is needed to clarify its mechanisms. Different types of dietary fats play distinct roles in fertility. Polyunsaturated fats, particularly DHA and EPA, support hormone regulation, ovarian follicle development, and embryo implantation, 23 while trans fats contribute to insulin resistance and inflammation, negatively affecting fertility. 24 A 2024 meta-analysis of two RCTs and nine cohort studies conducted in the U.S., Europe, and Asia (Korea, Japan) found that omega-3 intake, through supplementation or fish consumption, was associated with improved pregnancy and fertility rates, including in women undergoing fertility treatments. 25 The relationship between dairy intake and fecundability remains largely unclear, with no strong evidence of harm reported. 26 Some studies suggest differing effects between low-fat and high-fat dairy, but evidence is inconclusive. The only study on dairy and fertility outcomes, conducted within a U.S. fertility cohort, found a positive association with higher live birth rates but no association for any intermediate outcomes. 27 Epidemiological evidence on caffeine and fertility remains inconclusive due to study heterogeneity. Some prospective studies suggest that high preconception caffeine intake (≥300–600 mg/day) may slightly increase miscarriage risk. 28 The WHO states that caffeine consumption should be limited below 300 mg/day during pregnancy to reduce the risk of pregnancy loss and low birth weight. 29 The effect of alcohol on conception is unclear, with mixed findings reported in the general population. 30 In fertility treatments, alcohol use immediately before treatment may reduce success rates, while past-year consumption appears less harmful. 30 Alcohol consumption during pregnancy increases the risk of fetal alcohol spectrum disorders. 29 The WHO and national guidelines across Asia–Pacific countries consistently recommend women who are pregnant or planning pregnancy abstain from alcohol, as no safe level of consumption has been established. 29 , 31 In summary, nutritional status plays a crucial role in affecting fertility and birth rates. Healthy dietary patterns generally support reproductive health, but high-quality studies on specific foods or nutrients remain limited with inconsistent findings. Overall, maintaining a balanced diet rich in fruits and vegetables, whole grains, and healthy fats while limiting added sugars and avoiding alcohol may safeguard a successful pregnancy. Adequate folate intake is essential for reproductive health and NTD prevention. More research is warranted. Of note, diet is influenced by geographic, cultural, and socioeconomic factors. Since most existing research comes from North America and Europe, further studies are necessary to understand how dietary practices impact fertility and birth rates in other regions, including the Asia–Pacific. Physical activity, defined as any bodily movement produced by skeletal muscles that requires energy expenditure, is well-documented to enhance energy balance, cardiometabolic function, insulin sensitivity, weight regulation, and mental health, all of which positively influence reproductive health. 32 , 33 Evidence suggests a complex relationship between physical activity and reproductive health outcomes. The volume, intensity, and duration of physical activity all influence female fertility. 34 However, this area remains underexplored and controversial. Insufficient levels of physical activity include sedentary behaviour —characterised by prolonged sitting or low-energy activities—and physical inactivity , defined as an insufficient level of physical activity to meet health guidelines. 35 For adults, this means not achieving 150 min of moderate-to-vigorous-intensity physical activity per week or 75 min of vigorous-intensity physical activity per week. 32 A 2023 systematic review found that sedentary behaviours were associated with reduced female fertility in two out of seven studies, all conducted in Western populations. 36 Whether and how insufficient physical activity may influence female fertility remains unexplored, and high-quality research on this topic is lacking. Moderate-intensity physical activity , activity that burns 3 to 5.9 metabolic equivalents (METs), 37 requires a moderate amount of effort and slightly increases heart rate, such as brisk walking and recreational swimming. It has generally been shown to improve female fertility, 34 although null results on risks of ovulatory infertility and fecundability have also been reported. 38 , 39 A meta-analysis of five cohort studies, including one from China, found moderate-intensity physical activity, compared with low physical activity, was linked with 46% (risk ratio (RR) = 0.54, 95% confidence interval (CI): 0.38–0.77) reduction in infertility risk. 34 Among women with polycystic ovarian syndrome (PCOS), moderate physical activity may enhance fertility by improving insulin sensitivity and metabolic health, while vigorous physical activity may provide additional benefits for those who are overweight or obese. 40 Vigorous-intensity physical activity , activity that burns 6.0 METs or more, 37 such as running and fast cycling, requires a large amount of effort and leads to a substantial increase in heart rate and breathing. The role of vigorous activity in fertility remains controversial. Some studies suggest potential benefits; for example, a U.S. study of predominantly White women found a 5% reduction in the risk of ovulatory infertility for every additional hour of vigorous activity per week, even after adjusting for body mass index (BMI). 39 However, other evidence, mostly from European and North American populations, suggests that greater vigorous physical activity is associated with reduced fertility. 33 Interestingly, among individuals with overweight or obesity, some studies suggest that vigorous physical activity has either a beneficial or null impact on fertility. 41 Consistently, menstrual cycle disorders, such as functional hypothalamic amenorrhea, oligomenorrhea, and luteal phase deficiency, are more prevalent among athletes undergoing high training loads and body weight restrictions. 42 An important factor to consider is energy balance. Studies suggest that fertility disturbances linked to high-intensity physical activity stem not solely from the quantity of physical activity but rather from an imbalance between energy expenditure and intake. 43 This imbalance can lead to Relative Energy Deficiency in Sport, which disrupts sex hormone levels, causes anovulatory cycles, and induces amenorrhea, ultimately impairing fertility. 43 In addition to insufficient energy intake, insufficient sleep, low BMI, and heightened overall stress levels may all contribute to the disruption of female reproductive function. 33 This paradox—where greater physical activity improves health and slows ageing but does not necessarily enhance fertility—warrants further investigation. Physical activity may optimise pregnancy success among women with existing reproductive health issues. A 2019 systematic review and meta-analysis of 18 trial studies involving women with reproductive health problems, including four studies from Australia and the others primarily from Europe and North America, found that physical activity alone or in combination with diet is associated with higher clinical pregnancy (RR = 2.10, 95% CI: 1.32–3.55) and live birth rates (RR = 2.11, 95% CI: 1.02, 4.39), and higher conception rates and improved menstrual regularity in examined studies. 44 Notably, pooled data suggested similar outcome rates between intervention group and standard fertility treatments group. 44 Furthermore, another meta-analysis of over 3000 couples undergoing IVF or intracytoplasmic sperm injection (ICSI), based on eight studies from the U.S., Italy, Turkey, Iran, Brazil, and Australia, found that physically active women had nearly double the clinical pregnancy and live birth rates compared to their inactive counterparts, with no differences in miscarriage rates. 45 In summary, recreational physical activity shows promise in improving fertility capacity, particularly by lowering the risk of conditions associated with metabolic dysfunctions such as PCOS and obesity. However, most available evidence comes from studies conducted in Europe and North America, with limited and heterogeneous data from Asia. Additionally, there remains a lack of research in which physical activity is rigorously and consistently quantified, and heterogeneity in definitions limits generalisability and comparison across studies. Well-designed, large-scale studies across diverse populations are needed to better define the optimal “dose” and clarify the role of physical activity in supporting female fertility. Chronic stress elevates stress-related hormones, including corticotropin-releasing hormone, glucocorticoids (e.g., cortisol), prolactin, and thyroid hormones. These hormonal imbalances can disrupt the hypothalamic-pituitary-gonadal axis, which regulates reproductive function, potentially leading to menstrual irregularities and ovulatory dysfunction. 46 A 2017 systematic review of eight studies (none from the Asia–Pacific) found that women with a history of psychological stress had a higher risk of miscarriage. 47 Similarly, a prospective study conducted in the U.S. and Canada reported that severe depressive symptoms at baseline, regardless of treatment status, were associated with reduced fecundability, compared to no or low depressive symptoms. 48 A history of depression or anxiety, however, did not appear to impact fecundability, nor did the use of psychotropic treatments. 48 Women experiencing fertility issues generally report higher rates of anxiety and depression compared to their fertile counterparts. Prevalence estimates vary across populations but can be as high as 56.4% in India and 50.7% in China, according to previous fertility studies. 49 These symptoms are associated with factors like age, social and sexual concerns, maternal relationship stress, and financial difficulties. 50 Chronic stress, in turn, may lower their chances of achieving a successful pregnancy. A U.S. study found that higher self-reported perceived stress was associated with a monotonic, decreased probability of achieving a live birth among those who conceived through IVF. 51 A large Swedish registry-based study reported that a diagnosis of depression/anxiety or treatment with antidepressants before IVF was associated with reduced odds of pregnancy and live birth. 52 Notably, women with such a diagnosis without antidepressant treatment had more pronounced reductions in fertility outcomes, suggesting that the increased odds may be attributable to the underlying diagnosis or factors associated with the diagnosis, rather than the use of medication per se. In summary, the high prevalence of mental health symptoms and their negative impact on fertility highlight the critical need for integrating mental health care into routine preconception and fertility treatments. Addressing psychological distress early in the fertility journey may improve both natural conception and ART outcomes. In Asia–Pacific countries, the burden of psychological distress among women is likely underestimated due to cultural stigma, underreporting, and limited mental health resources, while its reproductive health impacts remain understudied. Region-specific research is warranted to address these data gaps. Globally, 30%–75% of individuals experience sleep deprivation (<7 h per day), with higher prevalence in some Asian countries. 53 Sleep disturbances are increasingly concerning, particularly among individuals undergoing fertility treatments. Circadian rhythms regulate reproductive hormones, and disruptions can alter hormone balance. Additionally, sleep patterns are influenced by menstrual cycle phases, highlighting the bidirectional relationship between sleep and hormonal regulation. 50 Research on sleep health and female fertility remains limited and heterogeneous, with most studies being cross-sectional or case–control in design. Sleep-related factors , including duration, quality, and night-shift work , have been examined in relation to female fertility, but findings are inconsistent. 54 , 55 , 56 While some studies found no significant associations between sleep duration and fertility, 54 others, including one cohort study conducted in China, suggested a U-shaped relationship, in which both long and short sleep durations were related to a higher risk of infertility. 56 Evidence on work shift patterns and long hours is more consistent but remains of low quality. A 2019 review found that attending fixed night shifts (vs. fixed day shifts) was associated with a 23% higher risk of miscarriage, based on 10 studies mostly from North America, Europe, and the Middle East; working more than 40 h per week was associated with a 38% higher risk of miscarriage, based on seven studies from North America and one from Australia. 55 A systematic review 56 further associated poor sleep quality, sleep disturbances, sleep apnoea, and certain chronotypes with reduced natural conception and lower clinical pregnancy and live birth rates. In summary, optimising sleep duration and quality appears important for reproductive success. High-quality, region-specific research, particularly from Asia–Pacific populations, is needed to better understand the role of sleep in reproductive and fertility health. A more comprehensive understanding of sleep during these critical periods, including its contributing factors, barriers, and effective interventions to improve sleep, should be a priority for future research. SES is related to patterns of fertility and birth rates. 57 Education , a key SES indicator, affects fertility rates by shaping access to employment opportunities, resources, and reproductive health knowledge. While both wealth and education are important predictors of fertility rates, their effects differ, and they interact with each other. 57 , 58 The association between wealth and fertility rates varies depending on a country's overall fertility level. In countries with high TFRs, wealth tends to have a positive association with fertility rates, whereas in countries with relatively low TFRs, the relationship is often negative. Education, however, has a more consistent and stronger inverse relationship with fertility rates: women with higher education levels tend to have fewer children across different contexts. 57 Additionally, education modifies wealth's impact on fertility rates. 57 Among highly educated women, greater wealth is often associated with lower fertility rates, while in groups with lower educational attainment, wealth tends to be linked to higher fertility. One key mediator between education and fertility rates is labour force participation. Higher educational attainment generally increases workforce involvement, reducing the number of births, particularly in low-fertility settings. 57 Although employment status alone may not be a strong predictor of fertility, it is more relevant in countries with low TFRs. 57 Moreover, the broader cultural and economic environment can shape how education and wealth influence fertility by shaping women's access to opportunities, knowledge, and resources during their reproductive years. 58 SES may also affect access to and outcomes of fertility treatments. A 2021 systematic review 59 analysing 11 studies from the U.S., U.K., Israel, and other European countries found that successful births from fertility treatments were more common among women with higher SES. However, results on the relationship between SES and fertility outcomes are mixed. Some findings indicate that higher income or education levels are associated with higher conception, clinical pregnancy, and live birth rates, while others show no significant differences. In summary, SES is a key social determinant of women's health, influencing fertility-related knowledge, intentions, access to resources, and potentially fertility and birth outcomes, with broader implications for population-level birth rates. Further research is needed to clarify the complex interplay between SES and other social factors in influencing fertility rates, especially in regions where evidence is limited, such as the Asia–Pacific. Strategies to address declining birth rates should be tailored to specific demographic and cultural contexts. Environmental pollution is increasingly recognised as a critical factor affecting female reproductive health, including air pollutants, endocrine-disrupting chemicals (EDCs), and heavy metals. In Asia, where rapid industrialisation has led to air pollution and environmental degradation, concerns over declining birth rates are growing. Countries such as China and India, which experience high levels of industrial emissions and air pollution, have frequently reported associations between pollutant exposures and adverse reproductive outcomes, including reduced fertility rates and increased miscarriage risks. 60 A similar threat persists in industrialised countries in Europe and North America due to trace residues of environmental contaminants. 61 A 2022 review of 11 studies highlighted the significant adverse health effects of toxic air pollutants , especially fine particulate matter (PM), nitrogen dioxide (NO 2 ), and sulphur dioxide (SO 2 ), linking them to an increased risk of infertility in both men and women, as well as a higher incidence of reproductive system cancers. 62 A 2021 narrative review suggested that exposure to PM (PM 2.5 and PM 2.5–10 ), ozone (O 3 ), and NO 2 is linked to reduced fertility and higher risks of early pregnancy loss, with increased infertility odds by 20% and decreased fecundity by 11% per 10 μg/m 3 increase of PM 2.5 . 63 EDCs are synthetic or naturally occurring chemicals that interfere with hormonal balance, potentially affecting fertility and pregnancy outcomes. Studies have linked EDC exposure to irregular menstrual cycles and increased rates of infertility. 64 , 65 For example, a review indicated that phthalates and their alternatives may disrupt female reproductive function by affecting the oestrous cycle, ovarian health, and subsequently lowering birth rates. 66 Microplastics and nanoplastics, primarily entering the body through ingestion, inhalation, and skin contact, have been found to target the reproductive system in a size-dependent manner, disrupting germ cell and somatic cell development. 67 Meanwhile, the use of pesticides in agriculture, even the trace presence of environmental residues in countries like the U.S., and Brazil that banned certain pesticides over half a century ago, still has a significant and long-term impact on fertility. 68 Heavy metals such as lead (Pb), mercury (Hg), and cadmium (Cd) are toxic environmental pollutants with severe reproductive consequences. A case–control study in China found that Pb and Cd exposures were associated with hormonal imbalances and menstrual irregularities, including an increased risk of PCOS. 69 , 70 Hg exposure, particularly concerning in coastal regions with high seafood consumption, was examined in a systematic review of 45 studies (13 from Asia, mostly from China), and was linked to reduced fecundability, higher prevalence and incidence rates of menstrual disorders, and longer time to pregnancy, resulting in reduced fertility rates. 71 The impact of heavy metal exposure on reduced fertility and fecundity is particularly pronounced in regions with high exposure levels, notably in China, India, and Bangladesh. 72 Environmental pollutants can negatively affect the success rates of IVF. For example, in a retrospective study of individuals undergoing IVF in Australia, exposure to NO 2 and O 3 was linked to lower live birth rates, and PM 10 was associated with an increased risk of miscarriage. 73 Similarly, a retrospective study of 11,148 IVF patients in China found that exposure to high levels of PM 2.5 , PM 10 , and SO 2 during the follicular phase was associated with lower clinical pregnancy and live birth rates and a lower number of high-quality embryos. 74 Additionally, a systematic review of 15 studies from Europe, North America, and the Middle East suggested that EDCs (e.g., polychlorinated biphenyls and organochlorine pesticides) impair embryo quality and pregnancy rates, whereas urinary triclosan concentrations were associated with decreased oocyte yield and longer time to pregnancy. 75 A study in Russia found that elevated cadmium levels were linked to a higher risk of having no blastocysts available for embryo transfer, while increased lead levels were associated with a 10% reduction in the rates of clinical pregnancy and live birth. 76 Air pollutants, EDCs, and heavy metals may reduce female fertility and birth rates by disrupting key reproductive processes. These exposures can interfere with hormonal regulation, impair ovarian function and folliculogenesis, and induce oxidative stress and inflammation, damaging reproductive tissues. 77 , 78 They may also alter epigenetic regulation and impair endometrial receptivity and placental function, increasing risks of implantation failure and early pregnancy loss. 79 In summary, environmental pollution, encompassing EDCs, heavy metals, and air pollutants, is a significant yet often overlooked factor contributing to declining birth rates. While socioeconomic and lifestyle factors remain central to reproductive trends, addressing environmental risks is essential for improving fertility and pregnancy outcomes. Notably, current literature reveals substantial gaps in understanding how environmental exposures affect reproductive health across racial and ethnic groups. Asian populations, especially those in the Asia–Pacific region, are underrepresented in large-scale epidemiological studies, despite experiencing disproportionately high pollution levels due to rapid industrialisation. These disparities limit the generalisability of existing findings and may hinder the development of region-specific public health strategies. Potential synergistic effects of multiple trace elements should also be considered in future research. 80 Over the past few decades, growing research has underscored the profound impact of weight, metabolic health, and pre-existing metabolic conditions such as diabetes, on fertility, fecundability, and pregnancy outcomes. These factors not only influence natural conception but also play a critical role in the success of ART and overall pregnancy outcomes, ultimately affecting the total birth rate at a population level. Obesity is one of the most well-documented factors negatively affecting female fertility. 81 A 2023 review by the International Federation of Gynaecology and Obstetrics and a committee commentary suggested that obesity reduces natural fertility and lowers clinical pregnancy and live birth rates following ovulation induction and ART procedures. 81 , 82 The mechanisms underlying these effects are multifaceted, involving hormonal imbalances, insulin resistance, and chronic inflammation, all of which can impair ovarian function, endometrial receptivity, and embryo quality. 83 In the Asian population, observational studies have found that women with overweight or obesity experience a 1.3–3.7 times higher risk of infertility compared to women with a normal BMI. 84 A preconception cohort in Singapore also showed that higher total body fat (%) was associated with a longer time-to-pregnancy. 85 While most studies to date have examined obesity in general, different forms of obesity with distinct underlying causes may influence female fertility through varied mechanisms and warrant targeted investigation and tailored prevention or treatment approaches. Lifestyle interventions targeting preconception weight loss have been explored as a potential strategy to improve reproductive outcomes. A systematic review and meta-analysis of 15 RCTs all stemmed from Western populations indicated that such lifestyle intervention achieved not only greater weight loss but also higher clinical pregnancy and live birth rates. 86 However, no beneficial effect of lifestyle interventions was observed on these parameters among individuals undergoing ART. 86 This suggests that while weight loss enhances natural fertility, its impact on ART outcomes may be more complex and warrants further investigation. In addition, a recent narrative review by the Global Obesity Collaborative suggested that weight loss resulting from bariatric surgery may have a beneficial effect on infertility. 87 For instance, post-surgical weight loss has been linked to restored ovulatory function, improved hormonal balance, and increased spontaneous conception rates. However, the evidence is still emerging, and further research is needed to fully understand the long-term reproductive outcomes and potential risks associated with bariatric surgery in women of reproductive age. Beyond obesity, other metabolic health phenotypes have been related to women's fecundability. A study from a multi-ethnic Asian preconception and pregnancy cohort found that metabolically unhealthy conditions such as metabolic syndrome and insulin resistance have adverse impact on fecundability in women across all BMI categories. 88 This finding suggests that metabolic health may be an independent determinant of fertility and underscores the need to address metabolic dysfunction in addition to weight management in women seeking to conceive. Insulin resistance , a hallmark of metabolic dysfunction, can disrupt ovarian function and lead to anovulation. This disruption is particularly evident in conditions like PCOS, where insulin resistance and obesity often coexist, further complicating reproductive outcomes. Interventions aimed at improving metabolic health may, therefore, have a dual benefit of enhancing both metabolic and reproductive health. Studies conducted from both Asian and White populations have shown that pre-existing diabetes , particularly type 2 diabetes, could significantly impact fertility and reproductive outcomes. It increases the risks of miscarriage, congenital anomalies, stillbirth, and perinatal mortality, 89 largely due to the harmful effects of hyperglycaemia on oocyte quality, embryonic development, and placental function. 90 Women with diabetes also commonly face coexisting conditions such as obesity and hypertension, further complicating pregnancy and ART success. 90 Therefore, comprehensive preconception care, including weight management, blood pressure control, and nutritional counselling, is essential for optimising reproductive outcomes and ensuring a healthy pregnancy in this population. In summary, metabolic health plays a key role in fertility and pregnancy outcomes, potentially influencing birth rates. Future research should clarify these mechanisms and identify effective interventions. Given the promising impact of lifestyle interventions—such as weight management and glycaemic control—on reproductive outcomes, a holistic approach to metabolic health is essential for women with sub-optimal profiles. Importantly, Asian women remain underrepresented in fertility research. Due to potential biological differences in ovarian reserve and reproductive ageing, as well as distinct dietary and lifestyle factors, future studies should prioritise greater inclusion of this population. Reproductive characteristics encompass biological factors and life-stage processes that potentially influence a woman's capacity to conceive, carry a pregnancy, and maintain overall reproductive health. These include reproductive complications, such as PCOS, endometriosis, and infections, as well as physiological processes like lactation, which can directly affect fertility health and indirectly shape fertility patterns and birth rates. Understanding these characteristics is important because they not only influence individual reproductive outcomes but also have broader implications for population-level fertility trends and maternal and child health. Several female reproductive complications have been linked to sub-optimal fertility phenotypes. These include irregular menstrual cycles, for example in clinical conditions such as PCOS; tubal factor infertility, commonly due to sexually transmitted infections (STIs) or pregnancy-related infections; and other gynaecological conditions affecting the female reproductive organs, such as endometriosis, adenomyosis, uterine fibroids, scarring, and congenital anomalies. These conditions, together with male-specific and couple-related fertility factors, contribute to the declining birth rates observed in human populations globally. PCOS affects an estimated 6–13% of reproductive-aged women, with up to 70% of affected women remaining undiagnosed worldwide. 91 PCOS is one of the most common causes of anovulation, leading to fertility difficulties, delayed childbearing, and lower birth rates. 92 A 2016 systematic review and meta-analysis based on 40 observational studies, including five from China and one from Japan, reported that PCOS was associated with higher risks of miscarriage, perinatal death, and pregnancy complications such as gestational diabetes and preeclampsia, 93 and these associations may not be entirely explained by obesity and/or age. Similarly, another systematic review of 29 observational studies, with 58.6% of the total sample being Asian and most using a retrospective design, found that among women undergoing IVF, those with PCOS had a higher risk of miscarriage compared to women with other causes of infertility. 94 Endometriosis affects approximately 10% of reproductive-aged women globally. 95 These women often experience severe, life-impacting pain during menstruation, sexual intercourse, bowel movements, and/or urination, 96 leading to chronic pelvic pain and subsequent mental and emotional health issues. Furthermore, about one-third of women with endometriosis experience difficulties conceiving. 97 In a U.S. study, endometriosis was associated with higher risks of spontaneous abortion and other pregnancy complications including gestational diabetes, hypertensive disorders of pregnancy, and preterm birth. 98 Observational studies from both Europe and China have also suggested that endometriosis is associated with lower live birth rates in women undergoing ART. 99 , 100 Although these two conditions both affect the ovaries, affected women often present with distinct symptoms. Women with PCOS generally have good ovarian reserve, but the condition is associated with comorbidities such as obesity and diabetes. These conditions should be optimised before assisting women with PCOS to conceive, as uncontrolled diabetes can negatively impact pregnancy. Diagnosing and providing individualised management for women with endometriosis can prevent delayed diagnoses and unnecessary surgical procedures, which may reduce ovarian reserve if ovarian endometriomas are excised improperly. Early fertility treatments for women with PCOS or endometriosis who desire to conceive are recommended to mitigate the impact of maternal ageing on reproductive outcomes. The WHO estimated 374 million new STIs globally in 2020, with chlamydia, gonorrhoea, syphilis and trichomoniasis as the leading infections. 101 STI rates vary widely across global regions, including within the Asia–Pacific. 101 If left untreated, these STIs can result in pelvic inflammatory diseases in women, causing damage to the fallopian tubes and contributing to tubal factor infertility. Tubal factor infertility accounts for 30% of female fertility problems. Additionally, tubal damage from STIs may negatively impact pregnancy outcomes. 102 Promoting sexual and reproductive health education is essential to prevent the acquisition of STIs by encouraging safe sexual practices, condom use, and timely access to early diagnosis and treatment. In summary, understanding the role of common female reproductive complications on fertility is critical for developing strategies to prevent modifiable risk factors of infertility, such as STIs and pelvic infections, and to diagnose and manage gynaecological conditions early. Timely management can prevent unnecessary procedures and treatment delays that may otherwise compromise fertility. Optimising preconception health in women and addressing reproductive risk factors are vital to improving fertility outcomes and countering the already low total fertility rates observed worldwide. While existing evidence highlights the negative impact of reproductive complications on fertility and birth rates in Asian populations, substantial data gaps remain within the region. The relationship between lactation and birth rate is complex. On one hand, it is well known that lactation suppresses fertility during lactational amenorrhea. Suckling enhances the sensitivity of hypothalamus to the negative-feedback effects of estradiol. This leads to the suppression of the gonadotropin-releasing hormone/luteinizing hormone pulse generator and consequently inhibits follicle development in the ovaries. 103 As such, lactation can result in lower birth rates by improving birth spacing. It has previously been reported that if there was no lactation in Sub-Saharan African nations with high levels of lactation, there would be an estimated 50% additional births in these nations. 104 While lactational amenorrhea may decrease birth rate due to suppressed fertility, it is important to mention that shortening interpregnancy durations can lead to elevated risks of adverse perinatal outcomes, including preterm births, and possibly of fetal and early neonatal death. 105 On the contrary, lactational amenorrhea may protect against some risk factors of infertility, including endometriosis and the timing of natural menopause. In an animal study, the grade of growth of endometriotic implants regressed, and showed signs of decreased cellular activity in lactation when compared to the pregnancy period. 106 In epidemiological studies, pooled estimate from a recent meta-analysis, which included Western and Middle East populations, showed that lactation reduced the odds of endometriosis, although the authors reported high heterogeneity across the included studies. 107 Importantly, results from high-quality studies in the meta-analysis were consistent with a protective effect of lactation on endometriosis. Further, the duration of postpartum amenorrhea appears not to fully explain the inverse association between lactation and risk of endometriosis, suggesting effects of lactation through yet unknown mechanisms. 108 Lactational amenorrhea may also affect the timing of natural menopause, and as a consequence, influence overall reproductive longevity. As ovarian reserve is fixed at birth, suppression of ovulation and ovarian activity during lactational amenorrhea may translate to a slower rate of follicle decline and delay the onset of natural menopause. 109 Recent prospective studies generally agree that lactation is associated with a lower risk of earlier natural menopause, despite variations in how lactation and timing of menopause are defined. 110 Another way that lactation may exert effects on secondary infertility is through the ‘reset hypothesis’ which posits that lactation plays a crucial role in restoring the adverse cardiometabolic changes that arise during pregnancy. 111 Many of these adverse cardiometabolic changes, including insulin resistance and obesity, are risk factors for infertility. Studies have shown that lactation improves glucose metabolism during the postpartum period in animal studies. 112 Similar effects of lactation are also seen in nondiabetic women in the postpartum period, 113 as well as among women with gestational diabetes. 114 Lactation appears to improve glucose metabolism by diverting glucose for lactogenesis to meet the greater need for glucose metabolites required for milk production. 115 Obesity is another well-known risk factor of infertility and there is widespread belief that lactation promotes weight loss. 116 Studies of high methodological quality 116 along with a recent large-scale study 117 and research focused on women with obesity, 118 generally indicate a positive association between lactation and weight loss. However, a systematic review which included 45 observational studies, of which five were conducted in the Asia–Pacific region, concluded that there is insufficient evidence supporting this claim. 116 More robust studies are needed to assess the direct effect of lactation on postpartum weight. As lactation affects both mother and child, some studies have examined whether breastmilk consumption affects offspring fertility. Such studies remain scarce and findings have been inconsistent. 119 , 120 Most of this work has centred on the effects of lactation and subsequent development of endometriosis. A systematic review found mixed evidence of a protective association between lactation and endometriosis in the offspring. 120 Yet results from a recent meta-analysis, which included three case–control studies from China and one from Japan, suggest ingesting breastmilk significantly protects against endometriosis though the study heterogeneity was high. 107 These studies should be evaluated next to studies on infant formula consumption as it has been previously reported that formula-fed infants may be at higher risk of endometriosis than breastfed infants. 121 More robust studies are needed to understand the association and identify underlying mechanisms. In summary, lactation may affect birth rates and fertility in complex ways. While lactational amenorrhea suppresses ovulation and can improve birth spacing, indirectly reducing birth rates, it may also provide protective effects against pregnancy complications and infertility-related conditions such as endometriosis and early menopause. Additionally, lactation supports metabolic health through mechanisms like improved glucose metabolism and potential postpartum weight loss, though evidence on the latter remains mixed. Some studies suggest breastmilk consumption may affect offspring fertility, particularly in relation to endometriosis, but further research is needed to clarify these associations. Although some studies have examined the effects of lactation on fertility and birth rates in Asian populations and in the Asia–Pacific region, these groups remain underrepresented in the literature, highlighting a need for more inclusive and region-specific research.

While our understanding of the role of women's health and wellbeing in fertility and birth rates has advanced, significant gaps in knowledge remain, and effective interventions are lacking. Women's health is multifaceted, with various characteristics interacting and influencing each other rather than acting in isolation. In general, a healthy diet and lifestyle, sufficient high-quality sleep, and optimal mental wellbeing promote reproductive and metabolic health, supporting preconception wellbeing, successful pregnancies, and overall reproductive longevity. Meanwhile, broader systemic characteristics, such as SES, environmental chemicals and pollutants, and access to education and reproductive care, shape individual health behaviours and status, extending beyond individual control and requiring policy-driven interventions. In addition to metabolic and reproductive complications, other preconception diseases, such as thyroid disorders, which can impair female fertility by disrupting hormonal balance and menstrual regularity, 122 may also impact fertility, underscoring the importance of comprehensive preconception health assessment. Beyond its relevance to fertility, women's health benefits not only their own wellbeing, but also the health of future generations across the lifespan. 123 Notably, as most existing evidence is drawn from studies in White populations, the Asia–Pacific region remains underrepresented across nearly all domains of women's health and fertility research, limiting the generalisability of current findings and potentially obscuring region-specific drivers of fertility-related outcomes. Biological differences, such as ovarian reserve 124 and metabolic phenotypes, 125 as well as distinct cultural norms, may uniquely shape women's health trajectories in the region. Moreover, delayed diagnoses, underreporting of mental health issues, high exposure to environmental pollutants, and limited access to care in some low- and middle-income countries pose additional challenges. Inclusive, high-quality, evidence-based data from the region is urgently needed to identify key determinants and guide effective, localized interventions. Multidisciplinary endeavours, ranging from research, education, policy, advocacy, to economic investment, are warranted to address declining birth rates and promote reproductive wellbeing across the Asia–Pacific and beyond.

CZ conceptualized and supervised the work. JY, WWP, GY, JA, LL, and ZH drafted different sections of the manuscript. JY led the manuscript revisions. All authors provided inputs for critical revision of the manuscript. CZ provided funding support for the work. All authors had final responsibility for the decision to submit for publication.

Declining birth rates have become a global concern, with total fertility rate (TFR), the average number of children per woman, falling in many countries. 1 Recent projections indicate that by 2050, 76% of countries will have a TFR below the replacement level of 2.1 children per woman, rising to 97.1% by 2100. 2 This decline has profound implications for demographics, economies, healthcare, and the environment. Asian countries such as Japan, South Korea, Singapore, and parts of Europe, are already facing demographic shifts that pose economic and social challenges due to ageing populations. 2 Women's health and wellbeing play a crucial role in shaping birth rates, primarily through their influence on fertility, assuming an intention to bear children. In addition, complications after conception, such as pregnancy loss, may also impact birth rates. Broadly, systemic characteristics can influence women's health at the individual level. For example, socioeconomic status (SES) can shape fertility intentions, lifestyle behaviours, and health status ( Fig. 1 ). Within individual-level characteristics, lifestyle behaviours can affect certain health outcomes, such as body weight and metabolic health, further compounding reproductive challenges and influencing the chances of successful pregnancies and deliveries. Clinical conditions such as certain reproductive complications can also impair fertility. A holistic understanding of women's health is essential for addressing fertility challenges and developing strategies to support women's health and fertility outcomes, subsequently improving birth rates. Fig. 1 Conceptual framework of systemic– and individual–level characteristics of women's health influencing fertility and birth rates. Footnote: The relationship between women's health and birth rates is largely mediated through female fertility and fecundability, assuming an intention to bear children. Systemic–level characteristics may influence both individual–level lifestyle characteristics and health status. For example, socioeconomic status may shape fertility intentions, access to healthcare, and health behaviours, while environmental pollutants may directly impact behaviours and physiological health. At the individual level, lifestyle characteristics may influence certain health-related factors (e.g., body weight and metabolic health), while others, such as lactation, are shaped by a broader combination of biological, social, and environmental characteristics. Together, these characteristics relevant to women's health interact to influence fertility and fecundability, ultimately shaping birth rates at the population level. Conceptual framework of systemic– and individual–level characteristics of women's health influencing fertility and birth rates. Footnote: The relationship between women's health and birth rates is largely mediated through female fertility and fecundability, assuming an intention to bear children. Systemic–level characteristics may influence both individual–level lifestyle characteristics and health status. For example, socioeconomic status may shape fertility intentions, access to healthcare, and health behaviours, while environmental pollutants may directly impact behaviours and physiological health. At the individual level, lifestyle characteristics may influence certain health-related factors (e.g., body weight and metabolic health), while others, such as lactation, are shaped by a broader combination of biological, social, and environmental characteristics. Together, these characteristics relevant to women's health interact to influence fertility and fecundability, ultimately shaping birth rates at the population level. This review explores the complex interplay between women's health, fertility, and birth rates by examining key determinants of women's health and wellbeing: 1) lifestyle factors, including four major pillars: diet and nutrition, physical activity, mental wellbeing, and sleep; 2) SES; 3) environmental pollutants; 4) body weight and metabolic health; and 5) female reproductive characteristics, with a unique inclusion of lactation. In this review, we use the term “female fertility” to refer broadly to the capacity to conceive and achieve a live birth, encompassing outcomes such as time to pregnancy, clinical pregnancy rate, live birth rate, fecundability, and pregnancy loss. Some of these outcomes correspond to measures of fecundity, the biological capacity to have a live birth, 3 but our focus is on the broader concept of fertility health in women, consistent with established medical definitions and usage. 4 , 5 This review aims to capture major findings on the above-mentioned topics at the human population level, identifies knowledge gaps, particularly for the Asia–Pacific region, and offers directions for future research and guidance for policy makers.

ZH received funding support from the National Medical Research Council, Ministry of Health, Singapore. This funding source did not directly support the current study and played no role in the design, data collection, or writing of the manuscript. Others declare no competing interests.