Interpretation
We found no association between obesity and live birth when transferring a single euploid blastocyst embryo. Our results suggest that the negative impact of being overweight or obese may be related to embryonic aneuploidy. A prior meta-analysis showed that a high BMI did not affect the IVF clinical outcomes in donor oocyte recipients, which suggested that oocyte quality may be the most important factor in obese women [14]. Previous studies suggested metabolic alterations in the serum are reflected in the follicular fluid and that some of these alterations may affect oocyte quality with higher BMI both in vitro and in vivo [15-17]. In addition, one prospective cohort study showed that elevated follicular follicular free fatty acid (FFA) were associated with poor cumulus oocyte complex (COC) morphology [18]. Moreover, severe obesity is also associated with a greater prevalence of spindle anomalies and non-aligned chromosomes in failed fertilized oocytes [19].
Embryo aneuploidy, which is widely known to be the most important factor for negative outcomes, was not given enough attention in previous studies when comparing the live birth rate between obese and normal-weight women. Obesity has been reported to alter the early embryo metabolomic signature [20], raising the possibility of epigenetic mediated impairment of clinical outcomes.