Does Obesity Reduce the Odds of Success After a Frozen IVF Transfer?
Not by much, according to a French study of 958 women: clinical pregnancy rates were nearly identical between normal-weight and obese women in frozen transfers (about 22% both), unlike fresh transfers where obesity is linked to lower success, likely due to uterine receptivity differences from stimulation hormones.
Another post touching on fertility and weight -- but this time, some good news.
The study
Fresh IVF cycles are known to have lower success rates in obese women, thought to be due to uterine receptivity issues caused by ovarian stimulation hormones. Researchers from France set out to test whether the same holds true in frozen embryo transfer (FET) cycles, which skip that stimulation step at the time of transfer. They looked at 958 women who had a frozen transfer between 2012 and 2017 at a French fertility clinic, with all embryos transferred at the day-5 blastocyst stage. Women were grouped as normal weight (BMI 18.5-25) or obese (BMI 30+), deliberately excluding the "overweight" range in between. Both groups had similar embryo quality and similar rates of single-embryo transfer (84%).
So does obesity reduce success rates in frozen cycles?
Barely, if at all. Clinical pregnancy rate was nearly identical (about 22% in both groups). Miscarriage rate was slightly higher in obese women (10% vs. 7%) but within a reasonable margin. Live birth rate was nearly the same too (19% vs. 20%). The researchers suspect the difference in fresh cycles comes down to obese women's uterine receptivity being affected by ovarian stimulation hormones specifically -- a factor frozen cycles don't have to contend with. This is preliminary and needs confirmation, but it suggests frozen transfer could be a genuinely good alternative to a fresh cycle for obese women.
Reference
Prost et al. (2020). Human Reproduction, 35(4), 589–865. Female obesity does not impact live birth rate after frozen-thawed blastocyst transfer.
Common questions
Is a frozen transfer a better option for obese women undergoing IVF?
This preliminary research suggests it could be, since the lower receptivity linked to obesity in fresh cycles appears tied to stimulation-hormone effects that frozen cycles don't have -- but it needs confirmation from more studies before treating it as settled.