Effect of pre-pregnancy body mass index on neonatal outcomes in women undergoing autologous frozen-thawed embryo transfer

Maternal pre-pregnancy body mass index increases preterm birth (PTB), macrosomia, and large-for-gestational age of singletons after frozen-thawed embryo transfer cycles; early PTB and very low birth weight only increased in obese cases.

VOLUME 116, ISSUE 4, P1010-1019


Xiaoyan Yang, M.D., Beihong Zheng, M.S., Yun Wang, M.D. 



To investigate the associations between pre-pregnancy body mass index (BMI) and neonatal outcomes in women undergoing autologous frozen-thawed embryo transfer (FET).


Retrospective cohort study.


University-affiliated reproductive medical center.


A total of 16,240 women with singleton deliveries achieved by autologous FET.



Main Outcome Measure(s)

Neonatal outcomes included preterm birth (PTB), low birth weight (LBW), small-for-gestational age (SGA), large-for-gestational age (LGA), fetal macrosomia, and birth defects.


After adjusting for confounding factors, our study showed that in autologous FET cycles, the overweight women (23 kg/m2≤ BMI <27.5 kg/m2) were associated with increased rates of PTB (adjusted odds ratio [aOR], 1.226; 95% confidence interval [CI], 1.060–1.418), macrosomia (aOR, 1.692; 95% CI, 1.491-1.921), and LGA (aOR, 1.980; 95% CI, 1.715–2.286); and the obese women (BMI ≥27.5 kg/m2) were significantly associated with increased PTB (aOR, 1.503; 95% CI, 1.167–1.936), early PTB (aOR, 2.829; 95% CI, 1.679–4.765), very LBW (aOR, 3.087; 95% CI, 1.720–5.542), macrosomia (aOR, 2.325; 95% CI, 1.862–2.904), and LGA (aOR, 3.235; 95% CI, 2.561–4.085). The rate of SGA infants was higher in the underweight women (BMI <18.5 kg/m2) (aOR, 1.687; 95% CI, 1.375–2.071) than that in the normal-weight women (18.5 kg/m2≤ BMI ≤23 kg/m2). No significant difference was observed in the risk of birth defects between normal-weight cases and other BMI categories.


Among women undergoing FET, pre-pregnancy BMI affected neonatal outcomes of singletons. BMI in Asian categories for overweight and obese showed significant increases in PTB, macrosomia, and LGA; early PTB and very LBW only increased in obese cases. In addition, underweight status was associated with increased risk of SGA. In contrast, there was no association between pre-pregnancy BMI and birth defects in FET cycles.