Objective: To compare the incidence of spontaneous miscarriage in women with moderate to severe obesity to that in women with a normal BMI after sonographic confirmation of the foetal heart rate in the first trimester.
Methods: Women were enrolled in a prospective observational study at their convenience in the first trimester after an ultrasound confirmed an ongoing singleton pregnancy with foetal heart activity present. Maternal height and weight were measured digitally and BMI was calculated.
Results: In the 3,000 women enrolled, the miscarriage rate overall was 3.9% (n = 117). The mean gestational age at enrolment was 11.1 weeks. In the class 2-3 (BMI > 34.9 kg/m(2)) obese primigravidas the miscarriage rate was 11.3% (n = 8) compared with 2.7% (n = 24) in the normal BMI category (p = 0.003), and 3.7% (n = 5) in the class 1 obese category (not significant). In multigravidas, there was no increased rate of miscarriage among class 2-3 obese women compared with multigravidas in the normal BMI category. The mean body composition values showed that primigravidas who miscarried had both increased fat and fat-free masses compared with those who did not, but multigravidas who miscarried had a similar fat mass and fat-free mass with those who did not.
Conclusions: In women with sonographic evidence of foetal heart activity in the first trimester, the rate of spontaneous miscarriage is low. It was increased in moderate to severely obese primigravidas, but was not increased in other obese women compared to women in the normal BMI category.