UC San Diego

Background: Pregravid obesity and abnormal gestational weight gain added to the physiological stresses of pregnancy have been shown to be associated with increased risks of morbidity and mortality for both the infant and mother. However, their effects on placental health are still uncertain. The placenta and the umbilical cord facilitate the interchange of nutrients between the maternal-fetal dyad. Recent research suggests that the placenta influences the metabolic environment in utero, which can in turn affect birth outcomes. Therefore, understanding how obesity affects the health of the placenta is vital. Methods: This dissertation consists of three studies using data from the University of California San Diego Perinatal Biospecimen Repository Cohort. Study 1 evaluated the effect maternal BMI has on indicators of placental health and assessed GDM as a mediator within the casual pathway. Study 2 assessed the effect gestational weight gain has on indicators of placental health. Study 3 built upon results from the first study by stratifying analyses to determine if the effect of maternal BMI on indicators of placental health were modified by fetal sex. The attenuation of the effect of obese maternal BMI on placental outcomes in the presence of chronic villitis was also evaluated in Study 3. Results: We found that maternal obesity was significantly associated with increased risk of larger placentas, longer umbilical cords, and chronic villitis (Study 1). Women with excessive gestational weight gain were shown to have higher risks of longer umbilical cords, especially in pregnancies with male fetuses (Study 2). We found that in pregnancies with female fetuses, the risk of chronic villitis is increased in women with obesity while other measurements of abnormal placental health were not at an increased risk. This varied in pregnancies with male fetuses, where the risk of larger placentas and longer umbilical cords were increased in women with maternal obesity, but no increased risk of chronic villitis was reported (Study 3). Discussion: Maternal BMI and gestational weight gain are associated with indicators of placental health. Each can be used to help identify women at high risk for abnormal placentas and provide the opportunity for increased surveillance and early intervention.