Obesity Linked to Worse Pregnancy Outcomes After Frozen Embryo Transfer

ANAHEIM, Calif. -- Women with obesity had worse pregnancy outcomes after euploid frozen embryo transfer, but it may be other fertility issues, not weight, that's driving the relationship, according to a retrospective study.

Among a large cohort of women, a body mass index (BMI) of 50 or higher was associated with a lower clinical pregnancy rate compared with a normal BMI of 18.5-24.9 (46.5% vs 65.9%; adjusted OR 0.46, 95% CI 0.30-0.72), reported Jennifer Bakkensen, MD, a third-year fellow at Northwestern University in Chicago, during her presentation at the American Society for Reproductive Medicine annual meeting.

Higher BMI was also tied to lower live birth rates compared with normal BMI (37.2% vs 58.2%; aOR 0.43, 95% CI 0.27-0.68), and was linked to higher miscarriage rates (20% vs 11.4%, respectively), though not significantly.

When BMI was analyzed as a continuous variable, every 1-unit increase in BMI was associated with lower odds of clinical pregnancy (aOR 0.98, 95% CI 0.98-0.99) and lower odds of live birth (aOR 0.98, 95% CI 0.98-0.99; P<0.001 for both).

However, in a subanalysis of couples who had a sole diagnosis of male-factor infertility, the relationship between BMI and pregnancy outcomes was attenuated, suggesting that other factors may play a role, Bakkensen said.

When BMI was analyzed as a continuous variable among patients in this subgroup, the relationship between BMI and clinical pregnancy was no longer significant (P=0.19). However, there was a significant association between BMI and live birth (P=0.015), as well as BMI and pregnancy loss (P=0.038).

"That subanalysis suggests that it could be, at least in part, the associated infertility diagnoses with obesity, and not obesity alone, that are driving that trend," Bakkensen told MedPage Today.

Prior research has shown that women with obesity have lower live birth rates and higher miscarriage rates after in vitro fertilization. However, data describing the association between BMI and pregnancy outcomes after frozen embryo transfer are lacking.

Bakkensen's group aimed to evaluate the association between BMI and pregnancy outcomes among women who underwent euploid frozen embryo transfer, using first single autologous frozen embryo transfers from a national cohort of women in the Society for Assisted Reproductive Technology Clinic Outcome Reporting System database from 2016 to 2019.

They assessed pregnancy outcomes across several BMI categories, ranging from less than 18.5 to over 50, and evaluated clinical pregnancy rates, pregnancy losses, and live birth rates in each group. All embryo transfers included in the analysis underwent preimplantation genetic testing, controlling for embryonic factors that could lead to implantation failure or pregnancy loss.

The analysis included 56,564 women, of whom 55% had a normal BMI, 24% were overweight, 10% had class 1 obesity, 5% had class 2 obesity, 2% had class 3 obesity, and less than 1% had class 4 obesity.

The mean age at transfer increased slightly across BMI groups, ranging from 34 in the lowest BMI category to 36 in the highest. Incidence of polycystic ovary syndrome (PCOS) also increased with increasing BMI.

Bakkensen said that this study was limited by its retrospective design, as well as its inclusion of relatively few patients with class 3 and class 4 obesity.

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