A correlation between the body weight of women undergoing IVF and the gender of offspring

Abstract

Research QuestionIs there an association between the weight of women and the gender of offspring generated from fresh and frozen/thawed embryo transfer (FET) cycles? DesignA retrospective study of 2,670 autologous single embryo transfers (SETs) cycles performed between January 2018 and December 2021 in 2,198 patients. The study sample consisted of two groups: fresh embryo transfer (ET) with data from 786 couples undergoing their first IVF cycle and a FET group, where 780 had their first frozen/thawed embryo transfer after freeze all embryos approach, and the following 1104 FET after one unsuccessful embryo transfer (ET or FET). Both study groups were divided according to body mass index (BMI) into three sets: underweight patients (BMI <18.5 kg/m2), normal weight (BMI 18.5 – 24.99 kg/m2), and overweight (BMI ≥25.0 kg/m2) women. A ratio of male-to-female live birth (secondary sex ratio, SSR) was determined. The relationship between the BMI of women undergoing IVF and the gender of the baby was analyzed based on a categorical Bayesian regression. ResultsAfter 2,670 performed SETs, 960 babies, 483 (50.31%) males and 477 (49.69%) females, were born with an even SSR of 100.8. Also, within normal-weight patients, boys and girls were born with equal frequency after ET and FET (SSR: 112 and 108, respectively). However, a significant shift in SSR in outer groups of BMI study patients was observed. This shift indicated that boys were born significantly more often in the underweight patients after ET and FET (SSR: 350 and 131, respectively). In contrast, girls were born significantly more often in the group of overweight patients in the FET group (SSR: 63). Those trends continued when the FET group was narrowed down to patients with the first embryo transfer after the 'freeze all' strategy (SSR: 129 in underweight and SSR: 67 in overweight women, respectively). ConclusionsNo differences were observed in the SSR of babies born in the general study population and among patients within normal body weight. However, more boys are born in underweight women in both ET and FET groups. Importantly, along with the significant increase in the effectiveness of treatment in the FET group of overweight women, a significant increase in the birth of girls was observed. Regarding the results of our research, it seems reasonable in the analysis of IVF results to consider not only the fact of the live birth but also the gender of the born child.