Efficacy of platelet-rich plasma in the treatment of thin endometrium: a meta-analysis of randomized controlled trials

Background Thin endometrium (TE) is a common cause of female infertility in clinical practice. Platelet-rich Plasma (PRP) therapy becomes a novel treatment for thin endometrium; however, its clinical application remains controversial. This meta-analysis aims to evaluate the therapeutic effects of intrauterine autologous PRP infusion in women with thin endometrium through relevant randomized controlled trials (RCTs).

We systematically searched studies published in English from inception until June 2024 in databases such as PubMed, The Cochrane Library, Embase, Web of Science, and MEDLINE. Search terms included “Platelet-Rich Plasma,” “thin endometrium,” “endometrial thickness,” “infertility,” “pregnancy,” “reproduction,” and “adverse reactions” . RCTs identified through the search were subjected to systematic review and meta-analysis, and data were analyzed using fixed-effects or random-effects models based on heterogeneity.

Eight RCTs involving 678 patients with thin endometrium were included. Patients receiving PRP infusion demonstrated significantly superior outcomes compared to the control group in endometrial thickness (MD: 1.23, 95%CI: 0.87 to 1.59, P = 0.000), clinical pregnancy rate (RR: 2.04, 95%CI: 1.52 to 2.76, P = 0.000), live birth rate (RR: 2.46; 95%CI: 1.57 to 3.85, P = 0.000), cycle cancellation rate (RR: 0.46, 95%CI: 0.23 to 0.93, P = 0.000), and embryo implantation rate (RR: 2.71; 95%CI: 1.91 to 3.84, P = 0.000). There were no statistically significance in spontaneous abortion rate (RR: 0.85, 95%CI: 0.40 to 1.78, P = 0.659), chemical pregnancy rate (RR: 1.84, 95%CI: 0.72 to 4.72, P = 0.204) and endometrial vascular improvement rate (RR: 1.10; 95%CI: 0.89 to 1.38, P = 0.367) between the two groups. The limitations of this study includes that, we only included single lauguage for literature research, the sample size and heterogeneity which could cause criteria bias.

Intrauterine PRP infusion may be an effective and safe treatment for women with thin endometrium. Further high-quality, large-sample, randomized controlled trials are needed to validate the reliability of our results. Trial registration The review protocol is registered on PROSPERO with registration number CRD42023490421, and no modifications were made to the information provided at registration.

Meta-analysis, Platelet-rich plasma (PRP), Randomized controlled trials (RCTs), Thin endometrium Efficacy of platelet-rich plasma in the treatment of thin endometrium: a meta- analysis of randomized controlled trials Xinyuan Liu1,2, Chengyu Qian3, Xiaoyue Jiang1,2, Yue Zhou1,2, Xue Feng4, Yinyin Ding1,2, Jing Jin2, Minghui Hu1, Weiye Zhou2, Bei Liu2 and Huifang Zhou2* Page 2 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567

Receptive endometrium and a qualified embryo are indispensable for successful implantation and pregnancy. Various factors influence the endometrial function [ 1, 2], among them, endometrial thickness is critical for assess - ing endometrial receptivity [3] and predicting the success rate of live births [ 4]. It has been proved that [ 5], when the thickness of endometrium constantly lower than the threshold, the probability of repeated implantation fail - ure will arise intensely [ 6]. Therefore, insufficient endo - metrial lining represents a significant contributing factor to female infertility and cycle cancellation [ 7]. According to a large cohort study released by Rabin Medical Center in 2020, the incidence of thin endometrium is 6.08% [ 4], which highlights the importance of addressing the treat - ment of thin endometrium. It is well-established that the characteristics of thin endometrium involve insufficient cell proliferation and functional imbalance, a point validated by a single-cell sequencing study based on clinical samples [ 6]. The pri- mary pathological basis of thin endometrium [8] includes delayed growth of uterine glandular epithelium, high resistance in uterine artery blood flow, leading to a reduc- tion in the number of uterine glandular epithelial cells, decreased expression of vascular endothelial growth factor (VEGF), impaired blood vessel development, and restricted growth of the endometrium. Currently, conser- vative treatment options for thin endometrium include estrogen, gonadotropin-releasing hormone agonists, aspirin, and sildenafil, etc. However, these methods are associated with multiple side effects, poor patient com - pliance, and inadequate endometrial response [9– 11]. Platelet-rich Plasma (PRP), a platelet concentrate extracted from fresh whole blood, has been studied since the 1970s for its role in injury repair and promotion of proliferation [ 12]. It has been found widespread appli - cations in various medical fields such as dermatology [13– 15], orthopaedics [ 16– 18], dentistry [ 19, 20], and plastic surgery [ 21]. The mechanism of PRP in medical filed may relate to promote cell proliferation, improve the blood flow, secret anti-inflammatory cytokines and so on, which is essential for tissue regeneration and repair. In recent years, regenerative medical therapies like PRP have become a research focus in the field of reproduc - tion. Numerous clinical studies have demonstrated positive outcomes in the application of PRP for thin endometrium. In 2015, Chinese scholars [ 22] conducted intrauterine PRP infusion in five refractory thin endo - metrium patients, resulting in successful endometrial expansion and pregnancies. Based on the previous result, many researches had been conducted [ 23– 25], provid - ing a robust evidence for the effective treatment of thin endometrium with PRP . However, conflicting viewpoints have also emerged. A recent clinical study [ 26] randomly assigned 390 patients to Granulocyte Colony Stimulat - ing Factor (GCSF), PRP , and saline groups. Although the PRP group significantly improved endometrial vascu - larization, there were no significant differences in clini - cal pregnancy rate and live birth rate among the groups. Kim [ 27], in a prospective study, suggested that there was no statistically significant difference in endometrial thickness after PRP infusion compared to pre-treatment levels. Additionally, several reported studies included small sample sizes [22, 28– 30], posed a risk of bias. Con - sequently, despite the widespread use of PRP in treat - ing patients with thin endometrium undergoing assisted reproductive technologies, its efficacy remains contro - versial. Further research is needed to determine whether PRP can safely and effectively reverse thin endometrium. Considering previous systematic reviews and meta- analyses, conclusions have been drawn that intrauterine PRP infusion is a promising treatment for women with thin endometrium in assisted reproductive techniques. Still, problems persist regarding its uncertain efficacy, unclear adverse reactions, and a lack of high-quality studies [ 31– 35]. With recent advancements in clinical research, our goal is to conduct a meta-analysis by col - lecting randomized controlled trials to explore the effec - tiveness of PRP in the treatment of thin endometrium. We hypothesize that, compared to a placebo or other treatment methods, PRP treatment influences endome - trial growth positively.

This meta-analysis aim to address the effectiveness and safety of intrauterine PRP injection compared to a con - trol group (placebo or other treatment methods) in improving clinical outcomes post-assisted reproduction in women with thin endometrium. Literature search and protocol Computer searches were conducted in databases includ - ing Pubmed, The Cochrane Library, Embase, Web of Science, and MEDLINE. Clinical studies involving PRP treatment for thin endometrium in women were screened. The search period extended from the inception of the databases to June 8, 2024. A combination of sub - ject headings and free-text terms was used for the search. Additionally, manual searches of reference lists of rel - evant reviews and systematic studies were performed to avoid omissions. The search terms included “Platelet-Rich Plasma, ” “thin endometrium, ” “endometrial thickness, ” “infertility, ” “pregnancy, ” “reproduction, ” and “adverse reactions” . Appropriate search strategies were employed for each database, and an example of the Embase data - base search is presented in Table  1. The review protocol is registered on PROSPERO with registration number Page 3 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567 CRD42023490421, and no modifications were made to the information provided at registration. Inclusion criteria Research subjects The definition and cut-off for thin endometrium differ between studies(Table  2). According to clinical prac - tice guidelines from the Canadian Fertility and Androl - ogy Society and Chinese expert consensus on diagnosis and management of abnormal endometrium in assisted reproductive technology, women aged over 18 with thin endometrium, defined as endometrial thickness < 7  mm on the day of ovulation after the peak of natural cycle luteinizing hormone, the day of gonadotropin-releasing hormone injection in controlled ovarian hyperstimula - tion cycles, or the day of progesterone initiation in frozen embryo transfer cycles [36, 37]. Interventions The experimental group received either pure PRP treat - ment or a combination of PRP treatment with con - ventional hormone replacement therapy (HRT, which means estradiol valerate or suppository progesterone treatment). The control group received a placebo or HRT. Outcome measures Primary efficacy indicator: Endometrial thickness post- PRP or progesterone initiation in the frozen embryo transfer cycle. Secondary efficacy indicators: ① Chemical pregnancy rate. ② Clinical pregnancy rate. ③ Sustained pregnancy rate or live birth rate. ④Spontaneous abortion rate. ⑤ Cycle cancellation rate. ⑥ Implantation rate. ⑦ Endome - trial vascular improvement rate. Research type Randomized Controlled Trials. Exclusion criteria The exclusion criteria for literature were as follows: 1. Duplicate publications. 2. Studies combining other diseases with the research subjects. 3. Literature where other treatments interfered with the interpretation of causality for the final treatment. 4. Literature with incomplete data. 5. Inaccessible full-text literature. 6. Review conference abstracts, non-clinical studies involving animal experiments, cell experiments, etc. Data extraction After removing duplicates using EndNote X9 soft - ware, two evidence-trained researchers (XY Liu, CY Qian) independently read titles, abstracts, and full texts, extracted and summarized relevant information, excluded ineligible literature, collected qualified litera - ture, and downloaded full texts. The researchers cross- checked the data to prevent important information from being missing or disordered. In cases of disagreement, a third researcher (XY Jiang) was consulted for discussion, and verification was performed. The data extraction table was saved as a Microsoft Excel file and included: (1) Basic information about the included articles, such as title, first author, and publica - tion year; (2) Relevant information about the research subjects in the literature, such as sample size, age, inter - vention measures, and course of treatment; (3) Outcome indicators and related elements involved in the assess - ment of publication bias risk. Table 1 Embase search strategies No. Searches Results 1 ‘thrombocyte rich plasma’/exp 21,103 2 ‘platelet-rich plasma’:ab, ti 18,658 3 ‘platelet rich plasma’:ab, ti 18,657 4 ‘platelet-rich fibrin’:ab, ti 2,391 5 ‘plasma rich in growth factors’:ab, ti 416 6 prp: ab, ti 27,549 7 prf: ab, ti 6,903 8 prgf: ab, ti 534 9 endometri*:ab, ti 170,721 10 ‘thin endometri*’:ab, ti 793 11 ‘endometrial thickness’:ab, ti 6,297 12 infertility: ab, ti 98,064 13 pregnancy: ab, ti 642,256 14 reproduction: ab, ti 123,814 15 ‘adverse reactions’:ab, ti 58,104 16 #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7 OR #8 47,490 17 #9 OR #10 OR #11 OR #12 OR #13 OR #14 OR #15 1,009,427 18 #16 AND #17 1,026 Table 2 Different definitions of thin endometrium Maximum endometrial thickness(on an ultrasound scan) Stage Resource <7 mm on the day of ovulation or human chorionic gonadotropin (HCG) administration Chinese expert con- sensus [36] < 7 mm or < 8 mm on the day of human chorionic gonadotropin (HCG) administration Canadian clinical prac- tice guide- line [37] ≤ 6 mm during ovarian stimulation and on the trigger day in IVF cycles A large study from Rabin Medical Center [4] Page 4 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567 Inclusion evaluation The Cochrane Evaluation Manual 5.1.0 recommended bias risk assessment tools for the quality evaluation of RCTs. The assessment included seven items: generation of random sequences, allocation concealment, blinding of participants and personnel, blinding of outcome asses - sors, completeness of outcome data, selective reporting of results, and other biases. Two researchers (XY Liu, CY Qian) independently made judgments for each item as “low risk of bias, ” “high risk of bias, ” or “unclear. ” After completion, cross-checking was performed, and in case of disagreement, a third researcher (XY Jiang) was con - sulted. If all the above criteria were fully met, the quality rating was classified as (A) If partially met, it was rated as (B) If not met at all, it was rated as (C) Studies of low quality were excluded from this research. Statistical analysis Review manager 5.4 software was used for bias risk assessment and result visualization. Endometrial thick - ness was treated as a continuous variable, with mean dif - ference (MD) and its 95% CI representing the effect size. Other outcome indicators were binary variables, and rel - ative risk (RR) was used as the effect size. If there were three-arm trials, they were split into two-arm trials for analysis. Stata/SE 15.0 was used for heterogeneity testing. If I2 ≤ 50% and P ≥ 0.05, it indicated no significant statistical heterogeneity and a fixed-effects model was used for meta-analysis. If I2 > 50% and P < 0.05, it suggested sub - stantial heterogeneity among the studies, and a ran - dom-effects model was employed for meta-analysis. A significance level of P < 0.05 was considered statistically significant.

Summary of the literature search A total of 2154 articles were initially identified through the search, and an additional 25 articles were obtained through reference tracing, making a total of 2179 articles. After removing duplicates using EndNote X9 software, 1,308 articles remained. Following title, abstract, and full-text reviews, 1,113 irrelevant articles were excluded, leaving 195 articles. After further full-text readings, 8 English-language articles were finally included in the analysis. The literature screening process is illustrated in Fig. 1. Basic characteristics of the included articles and evaluation Eight RCTs involving 678 patients with thin endome - trium were included. The experimental group received PRP or combined HRT (333 participants), while the con - trol group received HRT or placebo (345 participants). The basic characteristics of the included studies are shown in Table  3. Random number table methods were mainly used for random grouping, and details regarding Fig. 1 Flow chart of the study search Page 5 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567 other biases were not explicitly described in most stud - ies. One study [ 25] implemented double-blinding, one study [38] implemented blinding for outcome assessors, and the rest did not specify whether blinding was imple - mented. All eight studies ensured the completeness of outcome data and had no selective reporting of results. The quality assessment of the two-arm trials is detailed in Figs. 2 and 3. Outcomes Endometrial thickness Seven studies [25, 38– 43] involving 608 patients reported endometrial thickness after intrauterine PRP injection. Due to significant heterogeneity ( I2 = 84.0%, P = 0.000) (Fig.  4), a random-effects model was used for analysis, revealing a statistically significant difference in endome - trial thickness between the PRP group and the control group (MD: 1.23, 95%CI: 0.87 to 1.59, P = 0.000) (Fig.  5; Table 2). One study [ 44] that only reported changes in endometrial thickness within the PRP group without intergroup comparison was not included. Chemical pregnancy rate Five studies [ 25, 39, 40, 42, 44] involving 383 patients reported the chemical pregnancy rate after intrauter - ine PRP injection. Due to significant heterogeneity (I2 = 77.6%, P = 0.000) (Fig. 6), a random-effects model was applied for analysis, showing no statistically significant difference in the chemical pregnancy rate between the PRP group and the control group (RR: 1.84, 95%CI: 0.72 to 4.72, P = 0.204) (Fig. 7; Table 2). Clinical pregnancy rate Seven studies [ 25, 38– 41, 43, 44] involving 603 patients reported the clinical pregnancy rate after intrauterine PRP injection. Meta-analysis showed a significant differ - ence in clinical pregnancy rates between the two groups (RR: 2.04, 95%CI: 1.52 to 2.76, P = 0.000), and there was Table 3 General characteristic of the included studies(n = 8) Author No. of patients (PRP vs. Control) Age (years, PRP vs. Control) Treatment Outcome Platelet-rich plasma (PRP) treatment Conventional therapy Eftekhar 2018 [39] 33/33 18 ~ 42/18 ~ 42 PRP (0.5-1 ml, 1-2times) + C Estradiol valerate (2 mg tid, D2-13; 10 mg qd, D14- 15) + Vaginal suppository progesterone (400 mg bid, 3 days) ①②③④⑤⑥⑦ Chang 2019 [38] 34/30 34.77 ± 0.75/32.64 ± 1.70 PRP (0.5-1 ml, 1-2times) + C Estradiol valerate (6–10 mg qd, D2-?) + Suppository progesterone (vaginal,200 mg qd + intramuscular injection, 40 mg qd) ①③⑤⑥⑦ Nazari 2019 [25] 30/30 33.93 ± 2.76/32.33 ± 4.79 Estradiol valerate (6 mg qd, D2-8; 8 mg qd, D9- 10) + PRP(0.5 ml, 2times, D11-12) + Vaginal supposi- tory progesterone (400 mg bid) Estradiol valerate (6 mg qd, D2-8; 8 mg qd, D9- 10) + Sham_catheter(D11-12) + Vaginal suppository progesterone (400 mg bid) ①②③⑥⑦ Coksuer, H 2019 [44] 34/36 29.41 ± 4.54/28.89 ± 3.91 PRP (1 ml) + C Ovulation induction + Estradiol valerate (6-12 mg qd, D1-?) + Vaginal suppository progesterone(400 mg bid) ①②④⑤ Abduljab- bar, H. S 2022 [42] 35/35 35.91 ± 4.49/34.63 ± 4.26 Receive PRP(0.5 ml, 1time) after OPU Not receive PRP ①② Efendieva, Z 2023 [41] 42/30 35.1 ± 4.2/33.9 ± 3.7 PRP (0.5-1 ml) HRT ①③④⑤⑥⑧ 38/30 35.4 ± 4.1/33.9 ± 3.7 PRP (0.5-1 ml) + HRT HRT ①③④⑤⑥⑧ 5/30 Not mentioned/33.9 ± 3.7 autologous endometrial cells suspended in PRP HRT ① Pandey, D 2023 [40] 59/58 29.2 ± 1.89/29.11 ± 1.89 PRP (0.5-1 ml) + C Ovulation induction + Estradiol valerate (6 mg qd, D8) + Vaginal suppository progesterone ①②③⑧ Yu, N 2024 [43] 55/23 37.9 ± 6.9/39.0 ± 6.6 PRP(Intrauterine Infu- sion-2 ml twice) + C The COH protocol + oral estradiol valerate (qd, D3-) + suppository progesterone (oral and vaginal for 5 daysc) ①②③⑦ 38/23 40.0 ± 5.9/39.0 ± 6.6 PRP(Hysteroscopic Injec- tion-2 ml in four directions) + C The COH protocol + oral estradiol valerate (qd, D3-) + suppository progesterone (oral and vaginal for 5 daysc) ①②③⑦ Ps: ①Endometrial thickness post-PRP or progesterone initiation in the frozen embryo transfer cycle. ② Chemical pregnancy rate. ③ Clinical pregnancy rate. ④Sustained pregnancy rate or live birth rate. ⑤Spontaneous abortion rate. ⑥ Cycle cancellation rate. ⑦ Implantation rate. ⑧ Endometrial vascular improvement rate. Page 6 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567 Fig. 3 Risk of bias summary (n = 8) Fig. 2 Risk of bias graph (n = 8) Page 7 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567 no significant heterogeneity among the studies ( I2 = 0.0%, P = 0.800) (Fig. 8; Table 2). Live birth rate Four studies [ 39, 41, 43, 44] involving 362 patients reported the live birth rate. The live birth rate in the PRP group was significantly higher than that in the con - trol group (RR: 2.46, 95%CI: 1.57 to 3.85, P = 0.000), and there was no significant heterogeneity among the studies (I2 = 0.0%, P = 0.650) (Fig. 9; Table 2). Spontaneous abortion rate Four studies [ 38, 39, 41, 44] involving 310 patients reported the rate of spontaneous abortion after preg - nancy. Meta-analysis showed no significant difference in the spontaneous abortion rate between the PRP group and the control group (RR: 0.85, 95%CI: 0.40 to 1.78, P = 0.659), and there was no significant heterogeneity among the studies (I2 = 0.0%, P = 0.763) (Fig. 10; Table 2). Cycle cancellation rate Four studies [ 25, 38, 39, 41] involving 300 patients reported the cycle cancellation rate. Due to significant heterogeneity ( I2 = 59.9%, P = 0.041) (Fig.  11), a random- effects model was used for analysis, revealing a signifi - cantly lower cycle cancellation rate in the PRP group compared to the control group (RR: 0.46, 95%CI: 0.23 to 0.93, P = 0.000) (Fig. 12; Table 2). Implantation rate Four studies [ 25, 38, 39, 43] involving 306 patients reported the implantation rate. The implantation rate in the PRP group was significantly higher than that in the control group (RR: 2.71, 95%CI: 1.91 to 3.84, P = 0.000), and there was no significant heterogeneity among the studies (I2 = 16.6%, P = 0.309) (Fig. 13; Table 2). Endometrial vascular improvement rate Two studies [40, 41] involving 227 patients reported the improvement of endometrial vascularization. Meta-anal - ysis showed no significant difference in endometrial vas - cular improvement rate between the PRP group and the control group (RR: 1.10, 95%CI: 0.89 to 1.38, P = 0.367), and there was no significant heterogeneity among the studies (I2 = 39.0%, P = 0.194) (Fig. 14; Table 2). Fig. 4 Forest plot displaying the EMT in the study group versus the control group Page 8 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567 Risk of bias assessment Due to the limited number of studies, a publication bias analysis for the above results was not performed.

This meta-analysis, including eight RCTs, aimed to assess the effects of intrauterine platelet-rich plasma (PRP) treatment on endometrial thickness, endometrial vascu - lar improvement, and subsequent pregnancy outcomes in patients with thin endometrium, compared to tradi - tional hormone therapy or placebo groups. The data syn - thesis consistently demonstrated that intrauterine PRP injection significantly increased endometrial thickness, improved endometrial receptivity, and enhanced chemi - cal pregnancy rate, clinical pregnancy rate, live birth rate, and implantation rate compared to the control group. Nearly half of the studies had follow-up data until suc - cessful childbirth, and no adverse events were reported in subjects treated with PRP compared to the control group. In assisted reproductive cycles, endometrial thick - ness persistently < 7  mm may result in the cancellation of frozen embryo transfer (FET) cycles and embryo implantation. Even if embryos are obtained, the risk of natural miscarriage is higher, reducing the likelihood of a sustained pregnancy. Properly increasing endometrial thickness before initiating progesterone in frozen embryo transfer cycles can help avoid these situations, making endometrial thickness a crucial criterion for evaluating treatment effectiveness. In the included studies, both groups had endometrial thickness below 7  mm before treatment, with the PRP group fluctuating between 4.66 ~ 6.32 mm and the control group fluctuating between 4.99 ~ 6.39 mm. Interestingly, the control group showed a slight increase in endome - trial thickness compared to the PRP group. However, the meta-analysis demonstrated an overwhelming advantage of endometrial thickness in the PRP group over the con - trol group ( P < 0.05), confirming the effectiveness of PRP in endometrial regeneration. Although Coksuer’s study [44] did not show the individual endometrial thickness of both groups, it reported a significant increase in endo - metrial thickness (10 mm) after PRP injection compared to before treatment (6.25 mm). The significant statistical heterogeneity in studies assessing endometrial thickness, Fig. 5 Forest plot displaying the EMT in the study group versus the control group(use random-effects models) Page 9 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567 Fig. 7 Forest plot displaying the chemical pregnancy in the study group versus the control group(use random-effects models) Fig. 6 Forest plot displaying the chemical pregnancy in the study group versus the control group Page 10 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567 treated as the primary efficacy indicator in this analysis, prompted the use of a random-effects model for analysis. This heterogeneity might be attributed to differences in PRP preparation methods, doses, frequencies, and study populations. While all studies reported PRP preparation through a two-step centrifugation process, the choice of anticoagulants varied. Eftekhar [ 39] and Chang [38] used acidic citrate A anticoagulant solution (ACDA), a com - monly used anticoagulant in clinical PRP preparation, effectively maintaining platelet activity but expensive. On the other hand, Pandey [ 40] opted for citrate-phos - phate-dextrose-adenosine (CPDA) as an anticoagulant, which is easily accessible and cost-effective but slightly less effective in maintaining platelet activity [45]. Regard- ing PRP dosage and frequency, only Nazari [ 25], Abdul- jabbar [42], Yu [43] and Coksuer [ 44] explicitly reported PRP doses. Other studies had PRP doses fluctuating between 0.5 and 1 ml, with the majority considering fur - ther injections based on changes in endometrial thick - ness after PRP administration (usually not exceeding two additional injections). Some studies [ 40, 41, 44] did not specify the number of PRP injections in the text. Regard - ing the study population, in Chang’s study [ 38], patients with inadequate endometrial growth after treatment could decide to cancel the current cycle or proceed with embryo transfer, potentially introducing bias compared to other studies. Pandey [ 40], Yu [ 43] and Coksuer [ 44] included patients who underwent ovulation induction treatment before PRP injection and existing meta-anal - yses [ 46] have shown that ovulation-inducing drugs like clomiphene can thin the endometrium, potentially off - setting the regenerative effects of PRP . Additionally, only two studies [25, 38] employed a blinded method for mea- suring endometrial thickness under ultrasound, enhanc - ing the credibility and reliability of their results, while the remaining studies did not mention blinding. Considering these factors, there may be some inherent risks associ - ated with the results. In the context of secondary efficacy indicators, the Platelet-Rich Plasma (PRP) group, when compared to the control group, demonstrates statistically significant dif - ferences in clinical pregnancy rate, live birth rate, cycle cancellation rate, and embryo implantation rate. How - ever, there are no significant differences in chemical pregnancy rate, natural miscarriage rate, and endome - trial vascular improvement rate. This discrepancy may be attributed to the fact that most studies in the control group adopted estrogen hormone therapy as a conven - tional treatment method for patients with thin endome - trium. These patients also received luteal phase support Fig. 8 Forest plot displaying the clinical pregnancy in the study group versus the control group Page 11 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567 Fig. 10 Forest plot displaying the spontaneous abortion rate in the study group versus the control group Fig. 9 Forest plot displaying the live birth rate in the study group versus the control group Page 12 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567 Fig. 12 Forest plot displaying the cycle cancellation rate in the study group versus the control group(use random-effects models) Fig. 11 Forest plot displaying the cycle cancellation rate in the study group versus the control group Page 13 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567 Fig. 14 Forest plot displaying the Endometrial vascular improvement rate in the study group versus the control group Fig. 13 Forest plot displaying the implantation rate in the study group versus the control group Page 14 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567 post-embryo transfer, which to some extent increased the occurrence of positive events for Human Chorionic Gonadotropin (HCG) two weeks after embryo transfer and mitigated the risk of miscarriage. It is crucial to note that a positive chemical pregnancy rate does not neces - sarily indicate successful embryo development; clinical pregnancy is confirmed only after ultrasound detection of fetal heartbeats, making it a more critical and reliable indicator than the chemical pregnancy rate. Addition - ally, only two studies addressed monitoring and statistical analysis of endometrial vascular blood flow status, high - lighting the need for further relevant clinical research to visually assess the improvement of endometrial blood flow in patients with thin endometrium following PRP infusion, providing a basis for understanding the mecha - nism of action of PRP . While previous studies have preliminarily confirmed the efficacy of PRP for thin endometrium, they suffer from a broad scope of study populations [ 47, 48] (includ- ing patients with repeated implantation failures), a lack of recent clinical research reports [ 31], and unclear side effects. Considering that randomized controlled trials are widely acknowledged as the best strategy for evaluating clinical treatment outcomes, we attempted to include all currently available randomized controlled trials, focusing specifically on premenopausal women with thin endo - metrium. Notably, none of the studies reported compli - cations or adverse events associated with PRP injection. Our meta-analysis results align with previous research findings, indicating that intrauterine PRP injection for thin endometrium is not only clinically effective but also safe and reliable. Our study indicates that PRP treatment for thin endo - metrium is effective, and its mechanism of action is outlined as follows. Firstly, PRP can increase endome - trial thickness by promoting cell proliferation. Existing research has demonstrated that PRP contains a substan - tial amount of growth factors and cytokines, such as epidermal growth factor (EGF), fibroblast growth factor (FGF), transforming growth factor (TGF), interferon-γ (IFN-γ), Cytokeratin (CK)18, CK19, Zona Occludin-1 (ZO-1), Ki-67, and Vimentin (Vim) [ 49, 50]. CK and Vim serve as markers for uterine epithelial and stromal cells, respectively, while Ki-67 is a marker for cell pro - liferation. Following intrauterine PRP injection, these factors are transported to the endometrium to enhance tissue regenerative capacity and accelerate endometrial cell growth. Secondly, PRP improves the blood flow sta - tus of the endometrium, promoting neovascularization. VEGF plays a crucial role in uterine vascular forma - tion and decidualization [ 51], serving as a core factor in regulating vascular permeability. After PRP treat - ment, the expression of VEGF significantly increases, suggesting its favourable role in vascular formation and blood circulation, laying the foundation for endo - metrial growth. Thirdly, PRP optimizes the function of the endometrium, increasing the likelihood of embryo implantation. Important factors involved in regulating endometrial function and development, such as homeo - box A10 (HOXA10), leukaemia inhibitory factor (LIF), and integrin β3, show increased expression with the use of PRP [52]. This improves endometrial receptivity, avoid- ing the occurrence of natural miscarriage. Additionally, most patients with thin endometrium undergo repeated uterine interventions, leading to a higher risk of inflam - mation and fibrosis in the uterine cavity. Activated PRP produces chemokines such as Chemokine C–C motif ligand 2 (CCL2), C-X-c motif ligand (CXCL) 8, CXCL10, Claudin-1 (Cla-1), which act as chemoattractants [ 50]. They play a role in reducing inflammatory reactions and downregulating fibrosis, stimulating the expression of uterine endometrial stem cell marker c-Kit (CD117), and expediting the natural healing process. This provides rel - evant evidence for reshaping and restoring the normal morphology and function of the endometrium. Recent basic scientific research [ 53] suggests that PRP may also inhibit the death of uterine epithelial cells by regulating processes such as iron death, autophagy, and pyroptosis, providing new insights into further exploring the mecha - nism of action of PRP .

of this study include the following: Firstly, we only had studies that were accessible in full and reported in English, which may lead to retrieval omis - sions, exclusion of literature written in other languages, and limitations in methods for accessing full text, war - ranting further exploration. Secondly, our meta-analysis only included eight studies without subgroup analysis, and the sample size may impose restrictions and influ - ence the statistical and credible nature of the results. Thirdly, we acknowledged that heterogeneity exists among different studies, possibly due to various factors such as the preparation method, concentration, dosage, timing of PRP , the skill and proficiency of clinical doc - tors, clarity of ultrasound equipment, and the number and quality of embryos transplanted per cycle. Fourthly, the longest follow-up in the included studies extended to the successful delivery of offspring, with no mention of the subsequent growth and development of the offspring. Consequently, it is challenging to assess the long-term safety of PRP for women of childbearing age and their offspring. Lastly, some of the included literature stud - ies inadequately elaborated on allocation concealment, blinding implementation, and research bias, leading to uncertainties or high-risk factors during the evaluation. Therefore, further large-scale, high-quality, multicenter, and rigorously designed randomized controlled trials are required for validation. Page 15 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567 To the best of our knowledge, this is the first study that focuses on patients with thin endometrium, incorporat - ing all available randomized controlled trials to explore the effectiveness and safety of PRP treatment for thin endometrium in a meta-analysis. Despite some limita - tions, we believe that the conclusions of this study can play a significant role in the clinical application of PRP .

In summary, our meta-analysis suggests that intrauter - ine injection of Platelet-Rich Plasma (PRP) may be a novel therapeutic approach for thin endometrium. It not only effectively increases endometrial thickness in patients with thin endometrium but also improves preg - nancy outcomes, with reported safety and the absence of adverse events. However, further validation is warranted through additional large-scale, high-quality, multicenter, and rigorously designed studies. Abbreviations PRP Platelet-Rich Plasma EMT Endometrial Thickness TE Thin Endometrium IVF In vitro fertilization EnMSCs Endometrial mesenchymal stem cells MD Mean difference RR Risk ratio mm Millimeter ml Milliliter RCT Randomized controlled trial ACDA Anticoagulant solution CPDA Citrate-phosphate-dextrose-adenosine VEGF Vascular endothelial growth factor EGF Epidermal growth factor FGF Fibroblast growth factor TGF Transforming growth factor IFN-γ Interferon-γ CK Cytokeratin ZO-1 Zona Occludin-1 Vim Vimentin HOXA10 Homeobox A10 LIF Leukemia inhibitory factor CCL2 Chemokine C–C motif ligand 2 CXCL C-X-c motif ligand Cla-1 Claudin-1

Not applicable. Author contributions X.L. completed the conception and design of the work. X.L., C.Q. and X.J. wrote the main manuscript text. X.L. , C.Q., X.J., and Y.Z completed the acquisition, analysis, and interpretation of data. X.F. and Y.D prepared Figs. 1, 2, 3, 4, 5, 6 and 7. J.J. and M.H. prepared Figs. 8, 9, 10, 11, 12, 13 and 14. W.Z. and B.L prepared Tables 1, 2 and 3. H.Z completed project administration and funded acquisition. All authors reviewed the manuscript. Funding National Natural Science Foundation of China (No. 82205167 and 81973898); Jiangsu province key research and development plan (Society Development) project (No.BE2021726); Outstanding Young Doctor program of Jiangsu Provincial Hospital of Traditional Chinese Medicine (No. 2023QB0114); Jiangsu Province Graduate Student Research and Practical Innovation Program (SJCX22_0720 and SJCX23_0779). Data availability The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request. Declarations Ethics approval and consent to participate Not applicable. Consent for publication Not applicable. Competing interests The authors declare no competing interests. Author details 1Nanjing University of Chinese Medicine, Nanjing, Jiangsu, China 2Affiliated Hospital of Nanjing University of Chinese Medicine (Jiangsu Province Hospital of Traditional Chinese Medicine), Nanjing, Jiangsu, China 3Affiliated Hospital of Xuzhou Medical University, Xuzhou, Jiangsu, China 4Shandong Tai’an Hospital of Traditional Chinese Medicine, Tai’an 271000, Shandong, China Received: 10 March 2024 / Accepted: 6 August 2024

1. Palomba S, Piltonen TT, Giudice LC. Endometrial function in women with polycystic ovary syndrome: a comprehensive review. Hum Reprod Update. 2021;27(3):584–618. 2. Hiraoka T, Osuga Y, Hirota Y. Current perspectives on endometrial receptivity: a comprehensive overview of etiology and treatment. J Obstet Gynaecol Res. 2023;49(10):2397–409. 3. Aghajanova L, Houshdaran S, Balayan S, Manvelyan E, Irwin JC, Huddleston HG, Giudice LC. In vitro evidence that platelet-rich plasma stimulates cellular processes involved in endometrial regeneration. J Assist Reprod Genet. 2018;35(5):757–70. 4. Simeonov M, Sapir O, Lande Y, Ben-Haroush A, Oron G, Shlush E, Altman E, Wertheimer A, Shochat T, Shufaro Y. The entire range of trigger-day endome- trial thickness in fresh IVF cycles is independently correlated with live birth rate. Reprod Biomed Online. 2020;41(2):239–47. 5. Liu KE, Hartman M, Hartman A, Luo ZC, Mahutte N. The impact of a thin endometrial lining on fresh and frozen-thaw IVF outcomes: an analysis of over 40 000 embryo transfers. Hum Reprod. 2018;33(10):1883–8. 6. Lv H, Zhao G, Jiang P , Wang H, Wang Z, Yao S, Zhou Z, Wang L, Liu D, Deng W et al. Deciphering the endometrial niche of human thin endometrium at single-cell resolution. Proc Natl Acad Sci U S A 2022, 119(8). 7. Kasius A, Smit JG, Torrance HL, Eijkemans MJC, Mol BW, Opmeer BC, Broek- mans FJM. Endometrial thickness and pregnancy rates after IVF: a systematic review and meta-analysis. Hum Reprod Update. 2014;20(4):530–41. 8. Miwa I, Tamura H, Takasaki A, Yamagata Y, Shimamura K, Sugino N. Patho- physiologic features of thin endometrium. Fertil Steril. 2009;91(4):998–1004. 9. Chen Y, Lan Y, Shu Q, Lei XN. New progress in the diagnosis and treatment of thin endometrium. China Med Pharm. 2022;12(02):42–5. 10. Siristatidis CS, Basios G, Pergialiotis V, Vogiatzi P . Aspirin for in vitro fertilisation. Cochrane Database Syst Rev. 2016;11:CD004832. 11. Sharara FI, Lelea LL, Rahman S, Klebanoff JS, Moawad GN. A narrative review of platelet-rich plasma (PRP) in reproductive medicine. J Assist Reprod Genet. 2021;38(5):1003–12. 12. Ross R, Glomset J, Kariya B, Harker L. A platelet-dependent serum factor that stimulates the proliferation of arterial smooth muscle cells in vitro. Proc Natl Acad Sci U S A. 1974;71(4):1207–10. 13. Shen J, Yu X, Zhuang Y, Kong Y, Zhao J, Yao Z. Clinical efficacy and safety of targeted injection of PRP with skin booster in the treatment of aging face. Biotechnol Genet Eng Rev 2023:1–17. 14. Tahir M, Shaikh S, Sanober A, Memon YA, Khan MP . The role of platelet-rich plasma in reducing Pain, Pruritus, and improving Wound Healing of skin graft Donor Site. Pakistan J Med Health Sci. 2023;17(3):371–3. Page 16 of 16 Liu et al. BMC Pregnancy and Childbirth (2024) 24:567 15. Wei W, Zhang Y, Long B, Zhang Y, Zhang C, Zhang S. Injections of platelet-rich plasma prepared by automatic blood cell separator combined with topical 5% minoxidil in the treatment of male androgenetic alopecia. Skin Res Tech- nol 2023, 29(7). 16. Divya K, Divyani P , Taruni T, Nagamani C, Rao AS. PLATELET RICH PLASMA (PRP) THERAPY FOR OSTEOARTHRITIS. Int J Appl Pharm. 2023;15(1):186. 17. Farmani AR, Nekoofar MH, Ebrahimi-Barough S, Azami M, Najafipour S, Moradpanah S, Ai J. Preparation and in Vitro osteogenic evaluation of Bio- mimetic Hybrid Nanocomposite scaffolds based on Gelatin/Plasma Rich in Growth factors (PRGF) and Lithium-doped 45s5 bioactive glass nanoparticles. J Polym Environ. 2023;31(3):870–85. 18. Kim JH, Park YB, Ha CW. Are leukocyte-poor or multiple injections of platelet- rich plasma more effective than hyaluronic acid for knee osteoarthritis? A systematic review and meta-analysis of randomized controlled trials. Arch Orthop Trauma Surg. 2023;143(7):3879–97. 19. Daly BJ, Sharif MO, Jones K, Worthington HV, Beattie A. Local interventions for the management of alveolar osteitis (dry socket): a Cochrane review. Dent Cadmos. 2023;90(1):13–25. 20. Zhang TS, Mudalal M, Ren SC, Zhou YM. Implant site development using titanium plate and platelet-rich fibrin for congenitally missed maxillary lateral incisors: a case report. World J Clin Cases. 2022;10(6):2015–22. 21. Xue X, Bian Y, Yang M, Wei W, Meng L, Zhang Q, Tao J. Evaluation of injectable platelet-rich fibrin produced by a simple twice-centrifugation method com- bined with vacuum sealing drainage technology in the treatment of chronic refractory wounds. Front Bioeng Biotechnol. 2022;10:979834. 22. Chang Y, Li J, Chen Y, Wei L, Yang X, Shi Y, Liang X. Autologous platelet-rich plasma promotes endometrial growth and improves pregnancy outcome during in vitro fertilization. Int J Clin Exp Med. 2015;8(1):1286–90. 23. Tandulwadkar S, Naralkar M, Surana A, Selvakarthick M, Kharat A. Autologous intrauterine platelet-rich plasma instillation for suboptimal endometrium in frozen embryo transfer cycles: a pilot study. J Hum Reproductive Sci. 2017;10(3):208–12. 24. Aghajanova L, Zhang A, Lathi RB, Huddleston HG. Platelet-rich plasma infusion as an adjunct treatment for persistent thin lining in frozen embryo transfer cycles: first US experience report. J Assist Reprod Genet 2023. 25. Nazari L, Salehpour S, Hoseini S, Zadehmodarres S, Azargashb E. Effects of autologous platelet-rich plasma on endometrial expansion in patients undergoing frozen-thawed embryo transfer: a double-blind RCT. Int J Reprod Biomed. 2019;17(6):443–8. 26. Elbanna WS, Elhinnawi Sr MA, Salem S, Hareedy AA, Azmy O. PLATELET-RICH PLASMA AND COLONY-STIMULATING FACTOR ARE NON SUPERIOR TO PLA- CEBO IN IMPROVING ENDOMETRIAL QUALITY DURING FROZEN EMBRYO ICSI CYCLES - A DOUBLE-BLIND RCT. Fertil Steril. 2023;120(4):e19. 27. Kim H, Shin JE, Koo HS, Kwon H, Choi DH, Kim JH. Effect of autologous platelet-rich plasma treatment on Refractory Thin Endometrium during the frozen embryo transfer cycle: a pilot study. Front Endocrinol (Lausanne). 2019;10:61. 28. Gangaraju B, Mahajan P , Subramanian S, Kulkarni A, Mahajan S. Lyophilized platelet-rich plasma for the management of thin endometrium and facilita- tion of in-vitro fertilization. JBRA Assist Reprod. 2023;27(1):55–9. 29. Agirregoikoa JA, de Pablo JL, de la Fuente M, Anitua E. Potential of plasma Rich in Growth factors (PRGF-Endoret) to enhance the efficacy of assisted Reproductive techniques in refractory cases. Cureus. 2022;14(7):e26623. 30. Zadehmodarres S, Salehpour S, Saharkhiz N, Nazari L. Treatment of thin endo- metrium with autologous platelet-rich plasma: a pilot study. Jornal Brasileiro De Reproducao Assistida. 2017;21(1):54–6. 31. Du J, Lu H, Yu X, Lü Z, Mi L, Zhang X. Efficacy and safety of platelet-rich plasma for the treatment of thin endometrium: a protocol for systematic review and meta-analysis. Med (United States) 2020, 99(3). 32. Kim MK, Song H, Lyu SW, Lee WS. Platelet-rich plasma treatment in patients with refractory thin endometrium and recurrent implantation failure: a comprehensive review. Clin Exp Reprod Med. 2022;49(3):168–74. 33. Lin Y, Qi J, Sun Y. Platelet-Rich plasma as a potential New Strategy in the Endometrium treatment in assisted Reproductive Technology. Front Endocri- nol 2021, 12. 34. Mouanness M, Ali-Bynom S, Jackman J, Seckin S, Merhi Z. Use of intra- uterine injection of platelet-rich plasma (PRP) for endometrial receptivity and thickness: a literature review of the mechanisms of Action. Reprod Sci. 2021;28(6):1659–70. 35. Shalma NM, Salamah HM, Alsawareah A, Shaarawy AS, Mohamed MR, Mani- rambona E, Abd-ElGawad M. The efficacy of intrauterine infusion of platelet rich plasma in women undergoing assisted reproduction: a systematic review and meta-analysis. BMC Pregnancy Childbirth 2023, 23(1). 36. Zhao J, Huang GN, Sun HX, Fan LQ. Chinese expert consensus on diagnosis and management of abnormal endometrium in assisted reproductive tech- nology. J Reprod Med. 2018;27(11):1057–64. 37. Liu KE, Hartman M, Hartman A. Management of thin endometrium in assisted reproduction: a clinical practice guideline from the Canadian fertility and Andrology Society. Reprod Biomed Online. 2019;39(1):49–62. 38. Chang Y, Li J, Wei LN, Pang J, Chen J, Liang X. Autologous platelet-rich plasma infusion improves clinical pregnancy rate in frozen embryo transfer cycles for women with thin endometrium. Med (United States) 2019, 98(3). 39. Eftekhar M, Neghab N, Naghshineh E, Khani P . Can autologous platelet rich plasma expand endometrial thickness and improve pregnancy rate during frozen-thawed embryo transfer cycle? A randomized clinical trial. Taiwan J Obstet Gynecol. 2018;57(6):810–3. 40. Pandey D, Bajaj B, Kapoor G, Bharti R. Intrauterine instillation of autologous platelet-rich plasma in infertile females with thin endometrium undergoing intrauterine insemination: an open-label randomized controlled trial. AJOG Glob Rep. 2023;3(2):100172. 41. Efendieva Z, Vishnyakova P , Apolikhina I, Artemova D, Butov K, Kalinina E, Fedorova T, Tregubova A, Asaturova A, Fatkhudinov T, et al. Hystero- scopic injections of autologous endometrial cells and platelet-rich plasma in patients with thin endometrium: a pilot randomized study. Sci Rep. 2023;13(1):945. 42. Abduljabbar HS, Hashim H, Abduljabar HH, Elnaeim AA, Abduljabar NH. The effect of autologous platelet-rich plasma treatment on in Vitro Fertilization/ Intracytoplasmic sperm injection and its impact on the Endometrium and clinical pregnancy rate. Cureus. 2022;14(8):e27913. 43. Yu TN, Lee TH, Lee MS, Chen YC, Chen CI, Cheng EH, Lin PY, Huang CC, Lee CI. Intrauterine infusion and hysteroscopic injection of autologous platelet-rich plasma for patients with a persistent thin endometrium: a prospective case- control study. J Clin Med 2024, 13(10). 44. Coksuer H, Akdemir Y, Ulas Barut M. Improved in vitro fertilization success and pregnancy outcome with autologous platelet-rich plasma treatment in unexplained infertility patients that had repeated implantation failure history. Gynecol Endocrinol. 2019;35(9):815–8. 45. Dhurat R, Sukesh M. Principles and methods of Preparation of platelet- rich plasma: a review and author’s perspective. J Cutan Aesthet Surg. 2014;7(4):189–97. 46. Gadalla MA, Huang S, Wang R, Norman RJ, Abdullah SA, El Saman AM, Ismail AM, van Wely M, Mol BWJ. Effect of clomiphene citrate on endometrial thick- ness, ovulation, pregnancy and live birth in anovulatory women: systematic review and meta-analysis. Ultrasound Obstet Gynecol. 2018;51(1):64–76. 47. Hu S, Jin Z, Tang Q. Effects of Intrauterine infusion of autologous platelet- rich plasma in women undergoing treatment with assisted Reproductive Technology: a Meta-Analysis of Randomized controlled trials. Geburtshilfe Frauenheilkd. 2023;83(4):453–62. 48. Maleki-Hajiagha A, Razavi M, Rouholamin S, Rezaeinejad M, Maroufizadeh S, Sepidarkish M. Intrauterine infusion of autologous platelet-rich plasma in women undergoing assisted reproduction: a systematic review and meta- analysis. J Reprod Immunol 2020, 137. 49. Jang HY, Myoung SM, Choe JM, Kim T, Cheon YP , Kim YM, Park H. Effects of autologous platelet-rich plasma on regeneration of damaged endometrium in female rats. Yonsei Med J. 2017;58(6):1195–203. 50. Kshersagar J, Kawale AA, Tardalkar K, Damle MN, Chaudhari LR, Sharma R, Joshi MG. Activated platelet-rich plasma accelerate endometrial regeneration and improve pregnancy outcomes in murine model of disturbed endome- trium. Cell Tissue Bank 2023. 51. Abu-Ghazaleh N, Brennecke S, Murthi P , Karanam V. Association of Vascular endothelial growth factors (VEGFs) with recurrent miscarriage: a systematic review of the literature. Int J Mol Sci 2023, 24(11). 52. Wang Y, Chen X, Mao L, Cui L, Bai W. Therapeutic effect of platelet-rich fibrin transplant on formation of thin endometrium. Exp Clin Transpl. 2021;19(6):600–8. 53. Mao Y, Wang M, Xiong Y, Wen X, Zhang M, Ma L, Zhang Y. MELTF might regu- late ferroptosis, pyroptosis, and Autophagy in Platelet-Rich plasma-mediated endometrial epithelium regeneration. Reproductive Sci. 2023;30(5):1506–20. Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.