Morbid obesity and pregnancy outcomes after single blastocyst transfer: a retrospective, North American study

Maternal obesity has been shown to affect reproductive function and pregnancy outcomes following in vitro fertilization. More recently, studies have demonstrated lower live birth rates after single blastocyst transfer (SBT) in patients who are overweight or obese. However, the impact of morbid obesity on pregnancy outcomes after SBT has not been well elucidated. The present study aimed to determine whether morbid obesity has a detrimental impact on pregnancy outcomes after SBT in a North American population.

A retrospective, cohort study including 520 nulliparous and multiparous women undergoing top-quality SBT between August 2010 and March 2014 at a University Health Centre in North America was conducted. Primary outcomes included: miscarriage rate, clinical pregnancy rate, and live birth rate. Subjects were divided into different BMI categories (kg/m²), including <20, 20-24.9, 25.0-29.9, 30-40, and 40 or more.

The miscarriage rate per pregnancy for each group, respectively, was 36, 64, 59, 61, and 50% (p = 0.16); the clinical pregnancy (per patient) rate per group was 36, 52, 38, 26, and 10% (p = 0.009); and the live birth rate (per patient) per group was 35, 50, 38, 26 and 10% (p = 0.03).

Morbid obesity is a strong and independent predictor of poor pregnancy outcomes in patients undergoing top-quality SBT.