Maternal and perinatal outcomes in nulliparous women with a booking body mass index exceeding 50 kg/m2.

Background: Women with a body mass index (BMI) >35 kg/m² carry an increased obstetric risk; however, the experience of the Class IV and above obese nulliparous women is less understood.

Aims: To describe maternal and perinatal outcomes in nulliparous women of booking BMI > 50 kg/m².

Materials and methods: A cohort study of 48 nulliparous women who delivered between 2015 and 2019 in a tertiary hospital and had a booking BMI > 50 kg/m². Obstetric outcome data was collated via electronic and written patient records. The relationship between mode of delivery and BMI was assessed using direct logistic regression. Multiple pregnancies and severe congenital malformations (n = 3) were excluded.

Results: The mean booking BMI was 53.7 kg/m² (SD 4.05) and mean maternal age was 30.4 years (SD = 5.7). Comorbidities included asthma (43%), essential hypertension (20%) and diabetes (61%). Antenatally, accuracy was compromised in 80% of morphology scans (n = 35). In the perinatal period, 33 women (68.8%) were induced compared to a spontaneous onset of labour in two (4.1%) women. There were nine elective caesarean sections (CS), five of which were for breech presentation. Of those who intended on vaginal delivery (n = 35), 51% (n = 18) had an emergency CS. In these women, the risk of CS increased by a factor of 1.36 for every one point increase in BMI > 50 kg/m². The average gestational age was 37.5 weeks (SD 2.4) with 14% (n = 6) experiencing preterm deliveries. The incidence of babies born >90th percentile for gestational age was 15 (34%).

Conclusion: Increased BMI impairs maternal and perinatal outcomes and significantly increases the risk of emergency CS. BMI > 50 kg/m² is associated with higher-level interventions and obstetric complications.