The incidence and impact of increased body mass index on maternal and fetal morbidity in the low-risk primigravid population

Objective. To determine the incidence and impact of increased body mass index (BMI) on maternal and fetal morbidity in the low-risk primigravid population. Methods. This was a prospective study with retrospective analysis of delivery outcome data. All low-risk primigravida who met the inclusion criteria during the recruitment period were approached. BMI was calculated using the formula weight/height squared. The participants were divided into five categories: 'underweight' (BMI < 20 kg/m(2)), 'normal' (BMI 20.01-25 kg/m(2)), 'overweight' (BMI 25.01-30 kg/m(2)), 'obese' (BMI 30.01-40 kg/m(2)), and 'morbidly obese' (BMI > 40 kg/m(2)). Maternal outcomes evaluated included gestation at delivery, onset of labor (spontaneous/induced/ elective cesarean section), length of labor, use of oxytocin and epidural, mode of delivery, and estimated blood loss. Perinatal outcome measures included infant birth weight (kg) and centile, gestational age, ponderal index, Apgar score < 7 at 5 minutes, cord pH < 7.1, presence of meconium grade 3 at delivery, degree of resuscitation required, admission to neonatal intensive care unit (NICU), and duration of stay. Results. One thousand and eleven women participated in the study. Complete outcome data were available for 833 women (82%). A significant difference was identified in gestation at delivery between the subgroups (p < 0.004). A significant positive correlation was identified between cesarean section rates with increasing BMI, even when gestation was controlled for (p=0.004). Similarly, women in the normal BMI group remained significantly less likely to have an infant requiring NICU admission than obese women (2.2% vs. 8.6%; p=0.011). Conclusion. High BMI is associated with longer gestations, higher operative delivery rates, and an increased rate of neonatal intensive care admission.