The effect of progesterone supplementation for luteal phase support in natural cycle frozen embryo transfer: a systematic review and meta-analysis based on randomized controlled trials

Importance: The necessity of progesterone supplementation for luteal phase support (LPS) in natural cycle frozen embryo transfer (NC-FET) cycles warrants further confirmation.Objective: To investigate the effect of progesterone supplementation for LPS on the reproductive outcomes of patients undergoing NC-FET cycles.Data sources: The PubMed, Ovid-Embase, Cochrane Library, Web of Science, CNKI, Wanfang, VIP, and CBM were electronically searched. The search time frame was from inception up to September 2022.Study selection and synthesis: Randomized controlled trials (RCTs) that used progesterone for LPS in NC-FET cycles, including true NC-FET cycles (tNC-FET) and modified NC-FET cycles (mNC-FET), were included. The counted data were analyzed using relative risk (RR) as the effect-size statistic, and each effect size was assigned its 95% confidence interval (CI).Main Outcome Measures: The primary outcomes were the live birth rate (LBR) and the clinical pregnancy rate (CPR), and the secondary outcome was the miscarriage rate.Results: Four RCTs were included, which involved 1116 participants. The results of the meta-analysis showed that progesterone supplementation was associated with increased LBR (RR, 1.42; 95% CI, 1.15-1.75; I-2 = 0%, moderate-quality evidence) and CPR (RR, 1.30, 95% CI, 1.07-1.57; I-2 = 0%, moderate-quality evidence) in patients undergoing NC-FET cycles. Subgroup analysis showed that progesterone supplementation was associated with higher LBR and CPR in tNC-FET cycles. However, no association was found between increased LBR and CPR in mNC-FET cycles. In addition, only one RCT reported that oral dydrogesterone had similar CPR and miscarriage rate compared with vaginal progesterone in mNC-FET cycles.Conclusion(s): Overall, moderate-quality evidence suggested that progesterone supplementation for LPS was associated with increased LBR and CPR in NC-FET cycles. Progesterone supplementation was associated with a higher LBR and CPR in tNC-FET cycles. However, the effectiveness of progesterone supplementation in mNC-FET cycles should be further verified by larger RCTs. Low to very low-quality evidence indicated that oral dydrogesterone and vaginal progesterone have similar reproductive outcomes in mNC-FET cycles, which requires further study, especially in tNC-FET cycles.