Main findings
In this retrospective cohort study of 821 women undergoing IVF with
euploid blastocyst embryo transfer, we showed that live birth was not
significantly different between obese and normal-weight women.
The prevalence of obesity continues to rise worldwide. The negative
consequences of obesity are identifiable in every organ system. Obesity
is a known risk factor for subfertility, miscarriage, feto-maternal
complications and long-term risks in adult life [9]. Obese women are
at particularly high risk for adverse pregnancy outcomes. Up till now,
the relationship between obesity and negative reproductive outcomes is
clear, but the mechanism by which obesity affects fertility remains
unclear. Data from large trials have demonstrated fewer normally
fertilized oocytes, lower pregnancy and live birth rates in obese women
[10]. We believe that our
study adds important information to the existing literature on
pre-pregnancy BMI. A large cohort study of 152,500 cycles similarly
reported significantly higher odds of cycle cancellation, pregnancy
failures with overweight women [11]. A systematic review and
meta-analysis found decreased pregnancy rates, increased gonadotropins
and a higher miscarriage rate in obese and overweight women. These
differences are evidence even at a BMI≥ 25 kg/m2[12].
Our study differs from previous studies on obesity and clinical outcomes
in three ways. First, most studies dealt with embryo transfer without
PGT-A. Theorizing that oocytes from obese patients are subject to
alterations in normal mitotic checkpoints leading to aneuploidy
[13]. Therefore, they cannot accurately elucidate the effects of BMI
on clinical outcomes in obese women. Second, many studies dealt with
obesity as a categorical variable. In contrast, in our study, BMI was
also analyzed as a continuous variable that allowed a subtle increase in
live birth. Third, some studies compared clinical outcomes in fresh
cycles. One possible mechanism suggested that endometrial advancement
induced by ovarian hyperstimulation in a fresh embryo transfer cycle,
resulting in embryo-endometrium asynchrony. Therefore, our study focused
on frozen embryo transfer cycles, which eliminate the negative effect of
controlled ovarian stimulation.