Impact of Supraphysiological Estradiol Serum Levels on Birth Weight in Singletons Born After Fresh Embryo Transfer

In assisted reproductive technology, high estradiol (E2) levels at trigger may increase the risk of low birth weight (LBW). Our objective was to investigate the impact of supra-physiological E2 levels at trigger, on the rate of LBW in singleton pregnancies following fresh embryo transfers (ET), in a center that typically employs the ‘freeze-all’ strategy in case of high E2 levels, to prevent ovarian hyper stimulation syndrome risk. A cohort study was conducted in a university hospital between November 2012 and January 2017. The main inclusion criterion was having a live birth (LB) singleton (≥ 24 weeks of gestation) after a fresh-ET. Four groups were defined according to the E2 level at trigger, as quartiles of the entire patient population. The main measured outcome was the rate of LBW. 497 fresh-ET led to LB. Mean E2 level was 1608.4 ± 945.5 pg/ml. The groups were allocated as follows: 124LB in the Group E2 < 25 percentile(p) (1106.5 pg/ml), 124LB in the Group E2 [25p-50p] (1106.5–1439 pg/ml), 124LB in the Group E2[50p-75p] (1440–1915 pg/ml), and 125LB in the Group E2 > 75p (>1915 pg/ml). There was no significant difference in the rate of LBW (Group E2 < 25p, n = 8/124, (6.5%); Group E2[25p-50p], n = 15/124, (12.1%); Group E2 [50p-75p], n = 13/124, (10.4%); and Group E2 > 75p, n = 10/12, (8.1%); ( p = 0.43)). After multivariate analysis, E2 level at trigger was not significantly correlated to the rate of LBW. In our cohort, E2 level on the day of hCG trigger was not associated with increased odds of LBW after fresh embryo transfers.