The greater incidence of small for gestational age newborns after gonadotropin‐stimulated in vitro fertilization with a supra‐physiological estradiol level on ovulation trigger day

INTRODUCTION Reproductive scientists have postulated various risk factors for lower birthweight following conventional gonadotropin stimulated in vitro fertilization compared to spontaneously conceived children: parental factors (age, health, duration of subfertility, and smoking habits); ovarian stimulation; laboratory procedures; the number of oocytes retrieved; and the number of embryos transferred. Our aim was to investigate the impact of gonadotropin stimulation and serum estradiol level on the risk of a newborn's being small for gestational age. MATERIAL AND METHODS We conducted a cohort study (2010-2016) of singletons (n = 155) born either after conventional gonadotropin stimulated in vitro fertilization (using ≥150 IU/d human gonadotropin for stimulation) or after natural cycle in vitro fertilization without any stimulation. We analyzed perinatal outcomes using birthweight percentiles, as they adjust for gestational age and sex. RESULTS The proportion of small for gestational age was 11.8% following conventional gonadotropin stimulated in vitro fertilization, and 2.9% after natural-cycle in vitro fertilization (P = 0.058). The odds of small for gestational age were significantly higher with supra-physiological estradiol levels in maternal serum on ovulation trigger day (unadjusted odds ratio 4.58; 95% confidence interval 1.35 to 15.55; P = 0.015). It remained significant after adjusting for maternal height, age, and body mass index (adjusted odds ratio 3.83; 95% confidence interval 1.06 to 13.82; P = 0.041). CONCLUSIONS We found an associated risk of children being born small for gestational age after conventional gonadotropin stimulated in vitro fertilization compared to natural-cycle in vitro fertilization. This higher risk is significantly associated with supra-physiological estradiol levels. We propose a reduction in the dosage of gonadotropin to minimize the risk of small for gestational age and future health consequences. This article is protected by copyright. All rights reserved.