Objective To investigate whether supraphysiological estradiol (E2) in controlled ovarian stimulation (COS) cycles affects the subsequent frozen‐thawed embryo transfer (FET) in terms of the neonatal birthweight. Design Retrospective cohort study. Setting University affiliated hospital. Population In all, 2066 patients undergoing FET cycles that resulted in live singleton births between July 2011 and Dec 2016. Interventions None. Methods Multivariable linear regression and logistic regression was used to evaluate the association between peak E2 and birthweight outcomes. Main outcome measures Birthweight, z‐score adjusted for gender and gestational age, and incidence of small‐for‐gestational‐age (SGA) and low birthweight (LBW) in singleton neonates derived from FET cycles. Results Adjusted for confounding factors, both the absolute birthweight and the z‐score of singletons following FET were negatively associated with peak E2 levels in COS. In comparison with the referent category (E2 ≤1500 pg/ml), the categories with E2 >3000 pg/ml had a significantly lower z‐score. The difference (95% CI) in estimated marginal mean of birthweights between referent category and highest E2 (>8000 pg/ml) category was 104.57 g (18.13–181.06). Multiple logistic regression analyses showed that the adjusted odds ratio (95% CI) for SGA and LBW in term singletons comparing patients with E2 >3000 pg/ml with those with E2 ≤3000 pg/ml was 2.44 (1.37–4.34) and 2.32 (1.01–5.40), respectively. Conclusions Peak E2 levels in COS cycles are negatively associated with the birthweight of singletons conceived through subsequent FET cycles. Tweetable abstract The birthweight following FET is affected by previous COS cycle.

Background While single embryo transfer (SET) is widely advocated, double embryo transfer (DET) remains preferable in clinical practice to improve IVF success rate, especially in poor prognosis patients with only poor quality embryos (PQEs) available in addition to one or no good quality embryos (GQEs). Furthermore, previous studies suggest PQE might adversely affect the implantation of a GQE when transferred together. This study aims to evaluate the effect of transferring an additional PQE with a GQE on the outcomes in poor prognosis patients. Methods A total of 5037 frozen-thawed blastocyst transfer (FBT) cycles between January 2012 and May 2019 were included. Propensity score matching was applied to control for potential confounders, and we used generalized estimating equations (GEE) models to identify the association between the effect of an additional PQE and the outcomes. Results Overall, transferring a PQE with GQE (Group GP) achieved significantly higher pregnancy rate (PR), live birth rate (LBR) and multiple pregnancy rate (MPR) than GQE only (group G). The addition of a PQE increased LBR in patients aged 35 and over and in patients who received over 3 cycles of embryo transfer (ET) (48.1% vs 27.2%, OR:2.56, 95% CI: 1.3–5.03 and 46.6% vs 35.4%, OR:1.6, 95% CI: 1.09–2.35), but not in women under 35 and in women who received less than 3 cycles of ET (48.7% vs 43.9%, OR:1.22, 95% CI: 0.93–1.59 and 48.3% vs 41.4%, OR:1.33, 95% CI: 0.96–1.85). Group GP resulted in significantly higher MPR than group G irrespective of age and the number of previous IVF cycles. Conclusions An additional PQE does not negatively affect the implantation potential of the co-transferred GQE. Nevertheless, the addition of a PQE contributes to both live birth and multiple birth in poor prognosis patients. Physicians should still balance the benefits and risks of DET.

Day 6 FBT is associated with increased birth weight and contributes to the incidence of LGA newborns in FBT.

Objective: To evaluate the effect of transferring a poor quality embryo (PQE) with a good quality embryo (GQE) on the outcomes in poor prognosis patients. Design: Retrospective cohort study. Setting: University-affiliated hospital. Population: A total of 5,037 FBT cycles between January 2012 and May 2019. Methods: Single FBT with GQE were defined as group G and double FBT with GQE plus PQE were defined as group GP. Propensity score matching was applied to control for potential confounders. Multivariate generalized estimating equations (GEE) models were used to identify the association between the effect of an additional PQE and outcomes. Main Outcome Measures: Live births and multiple pregnancies. Results: Group GP resulted in a significantly higher live birth rate (LBR) than group G in women aged 35 and over and in women who received over 3 cycles of embryo transfer (ET) (48.