Evaluating in vitro fertilization outcomes of patients with low body mass index following frozen-thawed embryo transfer

Objective: To determine the relationship between patients with a low body mass index (BMI; calculated as weight in kilograms divided by the square of height in meters) and in vitro fertilization (IVF) outcomes following frozen-thawed embryo transfer (FET). Methods: Retrospective cohort study including 12 618 women aged 20–46 years with an underweight (<18.5) or normal weight (18.5–24.9) BMI who underwent controlled ovarian stimulation for IVF in a private and academic IVF center between August 2002 and December 2019. Results: Anti-Müllerian hormone, peak estradiol levels, number of MII oocytes, and fertilized oocytes were greater in the underweight group compared with the normal weight group. The total required gonadotropin dose was lower in the underweight patients compared with the normal weight patients. MII, fertilization, blastulation, and euploid rates did not differ before and after adjusting for confounders between BMI groups. In a cohort of 316 patients who underwent preimplantation genetic testing for aneuploidy and single euploid FET, pregnancy loss, pregnancy, clinical pregnancy, and live birth rates before and after controlling for covariates were similar between groups. Conclusion: Although there are known fetal growth or obstetrical issues associated in patients with a low BMI, it is reassuring that these risks do not extend to embryologic or clinical outcomes from IVF treatment.