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

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? 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 ) 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. 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