Maternal obesity and its effect on placental cell turnover

Background: Maternal obesity is a frequent obstetric risk factor, linked with short- and long-term consequences for mother and child, including foetal overgrowth, growth restriction and stillbirth. The mechanisms underlying these pathologies remain unknown but likely involve the placenta. Aims: To study placental cell turnover in relation to maternal body mass index (BMI). Methods: Term placental villous tissue was randomly sampled from 24 pregnancies, with a range of maternal BMI of 19.5-49.6. Immunohistochemistry was performed for human chorionic gonadotropin, Ki67 and M30 and image analysis used to calculate syncytiotrophoblast area and proliferative and apoptotic indices. Results were compared categorically between women of BMI 18.5-24.9 (normal), BMI 30.0-39.9 (obese classes 1 and 2) and BMI 40+ (obese class 3) and continuously against BMI; p<0.05 by the Kruskal-Wallis test or linear regression was considered statistically significant. Results: Increased maternal BMI was associated with categorical (normal versus obese class 3 and obese classes 1 and 2 versus obese class 3, both p<0.05) and continuous (r(2) = 0.24, p = 0.016) reductions in the proliferative index and a continuous reduction (r(2) = 0.17, p = 0.047) in the apoptotic index. Discussion: Maternal obesity is associated with a dose-dependent reduction in placental villous proliferation and apoptosis which may increase susceptibility to adverse pregnancy outcomes.