Association between serum progesterone levels on the day of frozen-thawed embryo transfer and pregnancy outcomes after artificial endometrial preparation

BACKGROUND: Previous studies have examined that a range of optimal serum P level during the implantation period was associated with optimal live birth rates. However, those results obtained with vaginal or intramuscular route of progesterone administration for luteal phase support (LPS) alone. Is there a relationship between the serum progesterone (P) on the day of frozen-thawed embryo transfer (FET) with the likelihood of a live birth (LB) in artificial cycles (AC) when using a combination of oral dydrogesterone and vaginal progesterone for LPS? METHODS: This was a retrospective study of 3659 FET cycles with artificial endometrial preparation in a Chinese tertiary-care academic medical centre from January 2015 to February 2017. Endometrial preparation was performed using estradiol (E(2)) valerate (Fematon-red tablets) 8 mg/d beginning on day 3 of the cycle, followed by administration of P both orally (8 mg/d Fematon-yellow tablets) and vaginally (400 mg/d; Utrogestan). The primary endpoint was live birth rate (LBR). The association between the serum P level on the embryo transfer day and pregnancy outcomes was evaluated by univariable and multivariable logistic regression analysis. RESULTS: The LBRs according to the serum P quartiles were as follows: Q1: 35.7%; Q2: 37.4%; Q3: 39.1% and Q4: 38.9%. Logistic regression analysis showed that the odds of a LB were not significantly different between the low (P < 7.9 ng/mL) and high (P ≥ 7.9 ng/mL) progesterone groups before or after adjustment (crude OR = 0.89, 95% CI: 0.76–1.04; adjusted OR = 0.89, 95% CI: 0.75–1.04). CONCLUSION: The present study suggests that the serum P levels on the day of embryo transfer (ET) do not correlate with the likelihood of a LB in artificial cycles when using a combination of oral dydrogesterone and vaginal progesterone for luteal phase support. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12884-023-05596-4.