Role of estradiol level before progesterone start on outcomes of frozen embryo transfer; a systematic review and meta-analysis

Estradiol (E2) levels on the day progesterone starts may negatively impact implantation, ongoing pregnancy, and live birth rates in frozen embryo transfer (FET). Overall, while the picture isn't entirely clear, some evidence suggests maintaining estradiol levels within a specific range before starting progesterone might be beneficial for frozen transfer success. So we performed a systematic review and meta-analysis to find out the rate of pregnancy-related outcomes of frozen embryo transfer in different level of E2. This review was designed based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). A multi database search was conducted (PubMed, Web of Science and Scopus) from the earliest date of each database until the 21st of April 2024. Data on the included articles including author, year, type of study, patients number, age, hormones like LH, FSH, successful pregnancy, live birth rate, and miscarriage were retrieved by two independent investigators. We categorized the values of E2 into five groups due to various values reported by studies to understand it better consisting of "Up to 200 pg/mL", "200-500 pg/mL", "500-1000 pg/mL", "1000-2000 pg/mL", "2000-3000 pg/mL" and "more than 3000 pg/mL". A forest plot was used to present the pooled measure. The analysis was performed using Stats version 13. A total of 14 studies containing 16,040 patients were included in the analysis. Studies reported a pooled prevalence of 57% with E2 level up to 200 pg/mL for clinical pregnancy. Also, studies reported a pooled prevalence of 46% with 200-500 pg/mL E2 for live birth rate. The lowest rate of miscarriage (6%) was observed in patients with 1000-2000 pg/mL E2 We found that the best level of E2 for having successful clinical pregnancy is up to 200 pg/mL and live birth rate is 200-500 pg/ml so we can say that E2 less than 500 pg/mL is a suitable value for pregnant.