Increased body mass index associated with increased preterm delivery in frozen embryo transfers.

The present study was performed to investigate whether maternal body mass index (BMI) affected the live birth (LB) outcomes of frozen embryo transfers (FET) in patients who underwent freeze-all treatment cycles. The autologous intracytoplasmic sperm injection (ICSI) cycles with blastocyst freeze-all cycles performed between February 2015 and January 2016 were retrospectively investigated. The 1188 subsequent FET performed were grouped according to maternal BMI classes for analysis; underweight (<18.5 kg/m2; 3.5%), normal-weight (18.5-24.9 kg/m2; 40.1%), overweight (25.0-29.9 kg/m2; 33.7%), or obese (classes I-III; ≥30.0 kg/m2; 22.8%). Uni- and multivariate analyses were performed, with LB as the primary outcome measure. In the categorical analyses of only the single blastocyst transfers (SBT), positive pregnancy (PP), LB and total pregnancy loss (totPL) rates were similar in the maternal BMI classes; however, the preterm delivery (PTD) rate in the obese class was significantly higher. In the multiple logistic regression models, maternal age was the most significant predictor of LB (OR = 0.9, 95%CI (0.90-0.98), p = .006) and the maternal BMI was the most significant predictor of PTD (OR = 1.1, 95% CI (1.02-1.14), p = .010). In conclusion, maternal BMI was the most significant variable in the outcome of PTD, with obese female patients at an increased risk of PTD. Impact statement What is known already? Obesity is rising worldwide to epidemic proportions and is expected to continue rising in the foreseeable future. Overweight and obesity not only increases the morbidity and mortality in the female populations but also significantly increases the risks of infertility in the women of reproductive age. Body mass index (BMI) has been the most widely used measure to describe the body weight of infertile patients. What do the results of this study add? Underweight, overweight and obesity do not significantly contribute to live birth outcomes. Maternal BMI was a significant predictor of PTD, with obesity most significantly at risk of PTD. What are the implications of these findings for clinical practice and/or further research? The evidence suggests that the weight management policy remain unchanged in IVF practice, with weight loss recommended for both young and ageing infertile patients. Performing a 'therapeutic' freeze-all IVF in the patients with weight-associated infertility may be a more suitable treatment strategy.