Association of high Body Mass Index and postdates pregnancy

Obesity with its growing prevalence is a major public health problem influencing gestational age at delivery. Raised Body Mass Index (BMI) has been shown to be associated with significantly increased risk of prolonged pregnancy; which is an important contributor to perinatal morbidity and mortality. Obesity needs modified antenatal, intrapartum and postpartum care by obstetrician. Limited data is found regarding association of obesity with prolonged pregnancy and the same fact led us to search for this association.

This cohort study was carried out in Gynecology and Obstetrics department, MTI Lady Reading Hospital Peshawar from March 2020 to April 2021. Patients were enrolled in third trimester at 37 weeks of gestation with primary exposures of interest being either self-reported pre-pregnancy weight or obtained from first trimester antenatal record. Patients were divided into two classes based on BMI i.e., one with BMI <25 and other with BMI ≥ 25. Patients in both classes were followed till their delivery to determine outcome of gestational age at delivery.

Statistically significant difference between the two groups was seen at lower age range of 18-21 years(p-0.04) and higher age range of 39-42 years (p-0.0001). Statistically significant association was found between high pre pregnancy BMI and postdates pregnancy (OR: 4.93 ;95% CI: 1.98-12.26, p-0.001). Association of induction of labor with high pre pregnancy BMI was not significant. (OR 0.56, 95% CI: 0.21-1.48, P < 0.001). Higher rates of Instrumental deliveries(p-0.0005) and cesarean sections (p-0.0001) were seen in higher BMI group.

Higher pre-pregnancy BMI is associated with increased risk of postdates pregnancy.