Efficacy of an Extended 10-day Letrozole Regimen Compared to the 5-day Regimen in Enhancing Ovulation in Infertile Women with Polycystic Ovary Syndrome: A Randomised Controlled Trial.

Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders affecting reproductive-aged women, characterised by oligo- or anovulation, hyperandrogenism and polycystic ovarian morphology.[ 1 2 3 ] It affects approximately 8%–13% of women globally and is a leading cause of anovulatory infertility.[ 4 ] Ovulation induction remains the cornerstone of treatment for infertility associated with PCOS.[ 5 6 ] Letrozole, an aromatase inhibitor, has emerged as the first-line agent for ovulation induction in women with PCOS due to its superior efficacy over clomiphene citrate in terms of ovulation, pregnancy and live birth rates, as shown in multiple trials.[ 7 8 9 ] The usual letrozole regimen involves administering 2.5–5 mg daily for 5 days starting early in the menstrual cycle.[ 10 11 ] However, follicular response with the standard 2.5-mg, 5-day letrozole regimen remains suboptimal, particularly in clomiphene-resistant women, with ovulation observed in only 22.9% of cycles at this dose in a prospective interventional study, necessitating dose escalation in the majority of patients.[ 12 ] Recent studies have explored modifications in letrozole dosing schedules – either by increasing the dose or extending the duration – to overcome resistance and improve follicular development.[ 13 14 ] Extending the duration of low-dose letrozole administration may sustain intraovarian estrogen suppression longer, allowing more robust follicular recruitment while minimising adverse effects associated with higher doses.[ 15 ] Despite growing interest, the evidence regarding the efficacy and safety of extended letrozole regimens remains limited and inconclusive, with few adequately powered randomised controlled trials addressing this question directly. This gap in the existing literature warrants further investigation, particularly in population where letrozole is used extensively. The primary objective of this randomised controlled trial was to evaluate the efficacy of a 10-day extended letrozole regimen versus the 5-day regimen in improving follicular response amongst women with PCOS-related infertility.

A total of 80 women with PCOS were randomised equally into two groups: Extended 10-day regimen group (2.5 mg daily for 10 days) and 5-day regimen group (2.5 mg daily for 5 days). Participants underwent up to three ovulation induction cycles unless pregnancy was achieved earlier or the participant withdrew. In total, 147 cycles were completed across both groups – 62 cycles in the extended 10-day regimen group and 85 cycles in the 5-day regimen group. Baseline clinical and biochemical characteristics were comparable between the two groups [ Table 1 ]. The mean age of participants was 27.95 ± 3.58 years in the extended 10-day regimen group and 27.18 ± 2.91 years in the 5-day regimen group ( P = 0.205). The distribution of primary infertility was 65.0% and 70.0% in the 10-day and 5-day regimen groups, respectively ( P = 0.812). Duration of infertility, body mass index and hormonal profiles including FSH, luteinising hormone, anti-Müllerian hormone (AMH), prolactin and thyroid-stimulating hormone levels showed no statistically significant differences between groups, indicating well-matched baseline characteristics. PCOS phenotypes A and D were the most prevalent in the study population, accounting for 37.5% and 57.5% of participants, respectively. The distribution of PCOS phenotypes differed between the two treatment groups [ Table 2 ]. PCOS phenotype A was more common in the extended regimen group (47.5% vs. 27.5%), whereas phenotype D was more frequent in the standard regimen group (70.0% vs. 45.0%). This difference reached statistical significance for phenotype D ( P = 0.041). PCOS phenotype D was more frequent in the 5-day regimen group; however, baseline hormonal parameters and ovarian reserve markers were comparable between groups. Baseline clinical and biochemical characteristics w Wilcoxon–Mann–Whitney U -test, c Pearson’s Chi-squared test, t t -test. SD=Standard deviation, BMI=Body mass index, FSH=Follicle-stimulating hormone, TSH=Thyroid-stimulating hormone, AMH=Anti-Müllerian hormone, LH=Luteinising hormone, IQR=Interquartile range Distribution of polycystic ovary syndrome phenotypes in the 10-day and 5-day letrozole regimens f Fisher’s exact test. PCOS=Polycystic ovary syndrome Table 3 presents the follicular response rates per participant in their initial treatment cycle. In the 10-day regimen group, 34 of 40 women (85.0%) demonstrated a follicular response, compared to 21 of 40 women (52.5%) in the 5-day regimen group, a difference that was statistically significant ( P = 0.002). The follicular response was thus significantly higher in the extended 10-day letrozole group compared to the 5-day group. Follicular response in the first ovulation induction cycle c Pearson’s Chi-squared test (without continuity correction) Endometrial thickness during the first ovulation induction cycle was comparable between the two groups. The median endometrial thickness was 8.0 mm (Interquartile range [IQR] 7.05–8.95) in the 10-day regimen and 7.4 mm (IQR 6.9–8.0) in the 5-day regimen, with no statistically significant difference between groups (Wilcoxon–Mann–Whitney U test, P = 0.116) [ Table 4 ]. Secondary outcomes of ovulation induction in the 10-day and 5-day letrozole regimens a Requirement for letrozole dose escalation was assessed after the first ovulation induction cycle amongst all randomised participants, b Two participants in each group discontinued treatment after the first cycle and were therefore not eligible for gonadotropin therapy, w Wilcoxon–Mann–Whitney U -test, c Pearson’s Chi-squared test, f Fisher’s exact test. IQR=Interquartile range, HMG=Human menopausal gonadotropin, OHSS=Ovarian hyperstimulation syndrome Secondary treatment outcomes differed significantly between regimens. Letrozole dose escalation to 5 mg was required in a significantly higher proportion of women in the 5-day regimen group compared to the 10-day regimen group (47.5% vs. 15.0%, P = 0.002). None of the participants in the 10-day regimen group required gonadotropin therapy, whereas 15.8% of women in the 5-day regimen group required HMG ( P = 0.025) [ Table 4 ]. The incidence of multi-follicular development (defined as >1 dominant follicle ≥16 mm) was low and comparable between groups (9.67% vs. 8.23% of cycles, P = 0.776). No cases of OHSS were observed in either group [ Table 4 ]. Regarding pregnancy outcomes [ Table 5 ], clinical pregnancy rates per patient were similar between the extended regimen group (35.0%) and the 5-day regimen group (32.5%) ( P = 0.813). When analysed per ovulation induction cycle, pregnancy rates were 22.58% (14/62 cycles) in the extended regimen group and 15.29% (13/85 cycles) in the 5-day regimen group; however, this difference was not statistically significant ( P = 0.286). Pregnancy and clinical outcomes *Pregnancy rate per cycle calculated by dividing the number of pregnancies by the total number of ovulation induction cycles performed in each group, **Congenital anomaly rates are calculated per pregnancy, † RR not estimable due to zero events in the comparator group, c Pearson’s Chi-squared test, f Fisher’s exact test. CI=Confidence interval, RR=Relative risk The incidence of multiple pregnancies was low, with one case (7.1%) in the extended group and none in the 5-day group ( P = 1.000). Miscarriage rates were 35.7% (5/14 pregnancies) and 23.1% (3/13 pregnancies) in the 10-day and 5-day groups, respectively ( P = 0.678). Congenital anomalies were reported in one pregnancy in each group, corresponding to 11.1% in the extended regimen group and 10.0% in the standard regimen group, without a significant difference ( P = 1.000). Although a numerically higher proportion of women conceived in the first ovulation induction cycle in the 10-day regimen group compared to the 5-day regimen group (20.0% vs. 7.5%), this difference did not reach statistical significance ( P = 0.193) [ Table 6 ]. Conceptions in subsequent cycles were fewer, with five and one pregnancies occurring in the second and third cycles, respectively, in the 10-day regimen group and eight and two pregnancies occurring in the second and third cycles, respectively, in the 5-day regimen group. Conception rate in the first ovulation induction cycle f Fisher’s exact test. CI=Confidence interval, RR=Relative risk Given the relatively small sample sizes the study is not sufficiently powered to detect statistically significant differences in pregnancy rates and adverse outcomes such as multiple pregnancy, miscarriage, or congenital anomalies. Therefore, these findings should be interpreted with caution.

In this randomised controlled trial, the extended 10-day letrozole regimen significantly improved follicular response compared to the 5-day regimen in women with PCOS, with no notable increase in adverse outcomes such as OHSS. Although clinical pregnancy rates were similar between groups, the numerically higher first-cycle conception rate observed with the extended regimen suggests a potential improvement in cycle efficiency. These findings, supported by prior studies, suggest that an extended low-dose letrozole regimen may be a useful alternative to conventional protocols in improving follicular response in women with PCOS. Future studies with larger sample sizes, longer follow-up, and live birth as a primary endpoint are needed to validate these findings, further clarify the safety profile and define the clinical role of extended letrozole regimens within individualised ovulation induction strategies for women with PCOS. BK and AK conceptualised and designed the study. BK and AKJ were involved in data collection. MAK performed the statistical analysis. BK drafted the manuscript. AK contributed to methodology development and manuscript writing. RM and NM provided supervision and critically reviewed the manuscript. All authors approved the final version. There are no conflicts of interest. The datasets generated and/or analysed during the current study are available from the corresponding author on reasonable request. The authors declare that no artificial intelligence-based tools were used for data analysis or manuscript writing.

This randomised controlled trial demonstrated that an extended 10-day letrozole regimen significantly improved follicular response rates compared to the 5-day regimen in women with PCOS undergoing ovulation induction. The enhanced follicular response observed with the extended protocol aligns with the pharmacological rationale of prolonged aromatase inhibition, which allows sustained follicular stimulation without adversely affecting endometrial receptivity, as reflected by the comparable endometrial thickness between groups.[ 15 ] Our findings are supported by El-Aziz et al ., who reported greater number of mature follicles, improved endometrial thickness and increased pregnancy rates with a 10-day extended low-dose letrozole regimen compared to a shorter course.[ 14 ] Similarly, Zhu et al ., demonstrated that extending letrozole duration in a step-wise manner in letrozole-resistant PCOS resulted in a high cumulative ovulation rate exceeding 90%, without the need for exogenous ovulation triggers or an increased risk of OHSS.[ 16 ] Although the patient population in Zhu et al .’s study differed from ours in that all women were letrozole-resistant, the marked improvement in ovulation rates with extended regimens reinforces the biological plausibility of prolonged aromatase inhibition as an effective strategy in PCOS.[ 16 ] Comparable findings have been reported by Jahan et al . and Morad et al . who observed improved follicular development and ovulation rates with extended or low-dose prolonged letrozole protocols without significant differences in endometrial thickness.[ 17 18 ] Notably, Jahan et al . confirmed ovulation biochemically using mid-luteal progesterone, lending further support to the ovulatory advantage of extended regimens, although pregnancy rates remained comparable between groups – mirroring the pattern observed in our study.[ 17 ] Collectively, these findings suggest that extended letrozole regimens are associated with improved ovulatory response without compromising endometrial receptivity; however, this does not uniformly translate into higher pregnancy rates. In the present study, clinical pregnancy rates per patient and per ovulation induction cycle were comparable between the two regimens, consistent with reports by Jahan et al . and Ali et al .[ 17 19 ] In contrast, Mandelbaum et al . demonstrated that while crude per-cycle pregnancy rates were not higher with a 2.5 mg extended (10-day) regimen, regimens incorporating increased dose and/or extended duration achieved ovulation and conception significantly earlier, resulting in improved time-to-pregnancy outcomes.[ 20 ] The study by Mandelbaum et al . is particularly relevant, as it demonstrated that regimens incorporating either higher doses or longer duration of letrozole achieved ovulation significantly earlier and reduced time-to-pregnancy, even when cumulative ovulation rates were similar across regimens.[ 20 ] The heterogeneity in pregnancy outcomes across studies likely reflects variations in study design, sample size, patient characteristics, PCOS phenotypes and cycle monitoring or treatment protocols. Although our study was not powered to detect differences in pregnancy or live birth outcomes, the numerically higher first-cycle conception rate observed with the extended regimen suggests a potential advantage in reducing time-to-pregnancy, an outcome of significant clinical relevance for infertile couples. This observation aligns with the time-dependent analyses reported by Mandelbaum et al ., where extended regimens achieved earlier ovulation and conception.[ 20 ] An important clinical finding of our study was the reduced need for dose escalation and complete avoidance of gonadotropin use in the extended regimen group. This has practical implications, as gonadotropin therapy is associated with higher costs, increased monitoring burden and a greater risk of multi-follicular development.[ 1 8 9 ] Similar advantages have been highlighted in step-up and extended letrozole protocols in both PCOS and unexplained infertility population, where improved ovulation rates were achieved without a proportional increase in complications.[ 16 19 ] The extended regimen demonstrated a favourable safety profile, with no increase in multi-follicular development, OHSS or multiple pregnancy rates. This is consistent with large randomised trials and systematic reviews by Legro et al . and Franik et al ., which established letrozole as a safer alternative to clomiphene citrate with a lower risk of multiple pregnancy and OHSS.[ 8 9 ] Both Zhu et al . and Ali et al . similarly reported no increase in OHSS or serious adverse events with extended or step-up letrozole protocols, reinforcing the safety of prolonged aromatase inhibition.[ 16 19 ] Although a numerically higher miscarriage rate was observed in the extended regimen group in our study, this difference was not statistically significant and occurred in the context of small absolute numbers, consistent with the variable miscarriage rates reported in previous trials.[ 14 17 20 ] Isolated congenital anomalies were observed in one pregnancy in each group, with no statistically significant difference between regimens; given the small number of events, no causal association with letrozole duration can be inferred. An imbalance in PCOS phenotype distribution was observed in our study, with phenotype D being more prevalent in the 5-day regimen group. Given emerging evidence that PCOS phenotype may influence ovarian responsiveness, this imbalance may have contributed to differences in ovulatory outcomes and represents a potential confounder. Nevertheless, baseline hormonal parameters and ovarian reserve markers were comparable between groups, partially mitigating this concern. The strengths of this study include its randomised controlled design, prospective trial registration, standardised ultrasound monitoring and evaluation of both efficacy and safety outcomes relevant to routine clinical practice. The demonstration that extended low-dose letrozole can improve follicular response while reducing the need for dose escalation or gonadotropin therapy suggests a potentially cost-effective and patient-friendly strategy, particularly in resource-limited settings. Routine biochemical confirmation of ovulation using mid-luteal progesterone was not performed; ovulation was inferred from serial ultrasonographic evidence of dominant follicle development. Reliance on ultrasound-based surrogate markers represents a methodological limitation. In addition, the open-label design may have introduced performance and detection bias, although objective ultrasonographic criteria were used to assess the primary outcome. Other limitations include the modest sample size, unselected PCOS population, limited number of cycles, short follow-up duration and lack of live birth data, which together restrict definitive conclusions regarding long-term reproductive outcomes. Future adequately powered randomised trials stratified by PCOS phenotype and incorporating live birth as a primary outcome, are required to better define the optimal role of extended letrozole regimens in contemporary ovulation induction protocols. From a clinical standpoint, the present findings support a response-oriented approach to ovulation induction in women with PCOS. In an unselected PCOS population, extending the duration of low-dose letrozole may be considered as part of an individualised treatment strategy, guided by early follicular response and clinical judgement, rather than routine dose escalation or early initiation of gonadotropins. Such an approach may help optimise ovulatory response while maintaining a favourable safety profile, particularly in settings where reducing treatment burden and cost is clinically relevant.

This prospective, open-label, parallel-group randomised controlled trial was conducted at a tertiary care centre in North India between October 2023 and November 2024. The trial was prospectively registered with the Clinical Trials Registry - India (CTRI) (CTRI/2023/10/059166; date of registration: 26/10/2023), prior to recruitment of the first participant. Ethical clearance was obtained from the Institutional Review Board (IECPG-151/23.03.2023, RT-02/20.04.2023) and all participants provided written informed consent. The study was done in accordance with the Helsinki Declaration. Eighty infertile women aged 21–38 years diagnosed with PCOS according to the modified Rotterdam criteria (2003), requiring the presence of any two of oligo/anovulation, clinical or biochemical hyperandrogenism and polycystic ovarian morphology on ultrasound, were enrolled. Women aged 21–38 years fulfilling the diagnostic criteria for PCOS, with at least one patent fallopian tube and normal semen parameters in the male partner as per the World Health Organization semen analysis guidelines (2021), were included. Women were excluded if they were younger than 21 years or older than 38 years, had endometriosis, diminished ovarian reserve defined as anti-Müllerian hormone (AMH) <1.1 ng/mL and/or antral follicle count 10 IU/mL, uncontrolled thyroid disorders, hyperprolactinemia, non-classical congenital adrenal hyperplasia, prior ovarian surgery, or current or recent (within the past 3 months) use of hormonal contraception or insulin sensitizers. AMH and antral follicle count were assessed solely to exclude diminished ovarian reserve and were not used for the diagnosis of PCOS. Eligible participants were randomised in a 1:1 ratio into two treatment groups using a computer-generated block randomisation sequence with a block size of four. Allocation concealment was ensured using sequentially numbered, sealed, opaque envelopes, which were opened only after enrolment. Participants assigned to the extended regimen group received oral letrozole 2.5 mg once daily from cycle day 2 to day 11, while those in the conventional regimen group received oral letrozole 2.5 mg once daily from cycle day 2 to day 6. Participants who were amenorrhoeic received withdrawal bleeding with medroxyprogesterone acetate 10 mg daily for 5 days prior to initiation of ovulation induction. Baseline hormonal and biochemical investigations were performed prior to treatment initiation. Serum AMH was measured using an ultrasensitive AMH/MIS enzyme-linked immunosorbent assay (Roche Diagnostics), following the manufacturer’s protocol, with a reference range of 0.03-23 ng/mL. Medication adherence was reinforced during clinic visits and confirmed through pill counts and patient diary review. Participant recruitment, allocation, follow-up and analysis are summarised in the CONSORT flow diagram [ Figure 1 ]. CONSORT flow diagram Transvaginal ultrasonography was performed using a Voluson E6 ultrasound system (GE Healthcare) equipped with a 5–9 MHz transvaginal probe. All scans were conducted by trained sonographers with more than 3 years of experience in reproductive ultrasonography. Ultrasound monitoring commenced between cycle days 9 and 11 and was continued every 2–3 days to assess follicular growth and endometrial thickness. A follicular diameter of ≥16 mm was predefined as the criterion for follicular response. In routine clinical practice, the ovulation trigger was generally administered when the leading follicle reached 18–20 mm. Each participant was allowed up to three ovulation induction cycles unless pregnancy was achieved earlier or the participant withdrew from the study. A cycle was classified as non-responsive if, despite adequate endometrial development (typically ≥6–7 mm), no follicle demonstrated progression beyond 10 mm on serial ultrasonography after completion of the assigned letrozole regimen. Participants with no response in the first cycle received a higher dose of letrozole (5 mg daily, with the same duration as their assigned regimen) in the subsequent cycle. Gonadotropin therapy using human menopausal gonadotropin (HMG) at a dose of 75-150 IU intramuscularly was offered only after persistent non-response to the step-up letrozole dose, based on follicular monitoring. Cycles demonstrating development of at least one dominant follicle measuring ≥16 mm were classified as responsive cycles. Participants with responsive cycles received human chorionic gonadotropin 5000 IU intramuscularly to trigger ovulation, followed by timed intercourse 24–36 h later. The use of human chorionic gonadotropin was intended to ensure ovulation and standardise the timing of intercourse in this anovulatory PCOS population, as routine biochemical confirmation of ovulation was not performed. Pregnancy was assessed using a urinary pregnancy test 2 weeks after the ovulation trigger and subsequently confirmed by ultrasonography. Ovulation was inferred based on serial ultrasonographic evidence of dominant follicle development. Routine mid-luteal serum progesterone estimation was not performed due to logistical constraints and is acknowledged as a study limitation. The primary outcome was follicular response, defined as the development of at least one dominant follicle measuring ≥16 mm in diameter. Secondary outcomes included the need for letrozole dose escalation, requirement of gonadotropin therapy, endometrial thickness, occurrence of multi-follicular development, ovarian hyperstimulation syndrome (OHSS), clinical pregnancy rate, pregnancy rate per cycle, multiple pregnancy rate and miscarriage rate. The sample size was calculated to detect a clinically significant difference in follicular response between the two letrozole regimens, with no interim analyses or stopping guidelines. The study was not powered for pregnancy or live birth outcomes. Based on ovulation rates of approximately 60% reported by Legro et al. and Begum et al. , we anticipated a 25% improvement with the extended regimen (targeting ≥85% ovulation). With a 5% alpha error and 80% power, the required sample size was 40 patients per group. Categorical variables were expressed as frequencies and percentages, while continuous variables were reported as mean ± standard deviation or median with interquartile range, as appropriate. Normality was assessed using the Shapiro–Wilk test. Between-group comparisons were performed using the independent samples t -test or Wilcoxon–Mann–Whitney U test for continuous variables and the Chi-square test or Fisher’s exact test for categorical variables. Statistical analysis was conducted using SPSS version 25.0 (IBM Corp., Armonk, New York, USA), with P < 0.05 considered statistically significant.