Evaluating the Impact of Gestational Weight Gain Based on an Increase in BMI Class in Patients with Obesity During...

To evaluate the impact of BMI class increase during pregnancy on perinatal outcomes.

This retrospective cohort study from 2009 to 2022 included singleton pregnancies with a pre-gravid BMI ≥ 30 kg/m² that then increased ≥ 3 BMI points by the time of delivery. Patients without obesity and those who decreased BMI class were excluded. The primary composite outcome included fetal growth abnormalities, cesarean delivery, oligohydramnios, polyhydramnios, and stillbirth. Both superiority and equivalence analyses were performed.

16,835 pregnancies were included. The majority of patients were White/not Hispanic (80.3%) and multiparous (65.6%); co-morbidities increased as BMI increased. An increase from BMI class I to II led to more adverse outcomes than maintaining class I BMI (aOR 1.17, 95% CI 1.06, 1.28), and equivalent outcomes as those who had a pre-gravid class II BMI (adjusted 90% CI, -0.022, 0.019; p < 0.01). This increased odds of adverse outcomes doubled when the BMI increase from I to II occurred prior to 30 weeks gestation (aOR 1.34, 95% CI 1.21, 1.48). An increase from BMI class II to III led to higher odds of adverse outcomes than maintaining BMI class II (aOR 1.40, 95% CI 1.25, 1.58). The data does not provide sufficient evidence that the outcomes were equivalent to those with a pre-gravid BMI class III (adjusted 90% CI, -0.52, -0.017; p = 0.26).

For pregnant patients with obesity, recommendations for pregnancy management should be based on current BMI, rather than pre-gravid BMI.