Short term neonatal outcomes of pregnancies complicated by maternal obesity

Published:January 19, 2023DOI:
      • A
        Why was the study conducted? To evaluate whether a composite of neonatal mortality and short-term morbidity increases as maternal BMI at delivery increases.
      • B
        What are the key findings?
        • -
          Maternal comorbidities, including chronic hypertension, pre-gestational diabetes, and cesarean delivery are more frequent in higher BMI categories.
        • -
          Compared with the reference group (BMI 18.5-29.9 kg/m2), only neonates born to pregnant people with a BMI of 40-49.9 kg/m2 were at increased risk for composite morbidity.
      • C
        What does this study add to what is already known? After adjusting for other comorbidities, such as chronic hypertension, diabetes, preeclampsia/eclampsia and preterm birth, increasing maternal BMI is not associated with an increase in composite neonatal morbidity.



      Maternal obesity complicates a high number of pregnancies. The degree to which neonatal outcomes are adversely affected is unclear.


      To evaluate neonatal outcomes of pregnancies complicated by maternal obesity.

      Study Design

      Secondary analysis of a cohort of deliveries occurring on randomly selected days at 25 hospitals from 2008-2011. Data were collected by certified abstractors. This analysis included singleton deliveries between 24 and 42 weeks. BMI was calculated based on maternal height and most recent weight prior to delivery. Normal/overweight (reference group; BMI 18.5-29.9 kg/m2), obese (OB; BMI 30-39.9 kg/m2), morbidly obese (MO; BMI 40-49.9 kg/m2) and super morbidly obese (SMO; BMI ≥ 50 kg/m2) patients were compared. Patients in the reference group were matched 1:1 with those in all other obesity groups using the baseline characteristics of age, race-ethnicity, previous cesarean, pre-existing diabetes, chronic hypertension, parity, cigarette use, and insurance status. The primary outcome was composite neonatal morbidity, including fetal or neonatal death, hypoxic ischemic encephalopathy, respiratory distress syndrome, Grade III-IV intraventricular hemorrhage, necrotizing enterocolitis, sepsis, birth injury, seizures, or ventilator use. We used modified Poisson regression to examine the associations between BMI and composite neonatal outcome. Preterm delivery < 37 weeks and the presence of maternal preeclampsia/eclampsia were included in the final model because of their known associations with neonatal outcomes.


      52,162 patients and their neonates were included after propensity score matching. Of these, 21,704 (41.6%) were OB, 3787 (7.3%) were MO and 590 (1.1%) were SMO. A total of 2103 (4.0%) neonates had the composite outcome. Neonates born to pregnant people with morbidy obesity had a 33% increased risk of composite neonatal morbidity compared with those in the reference group (aRR 1.33; 95%CI 1.17-1.52), but no significant association was observed for persons with obesity (aRR 1.05; 95%CI 0.97-1.14) or with super morbid obesity (aRR 1.18; 95%CI (0.86-1.64).


      Compared with the reference group, gravidas with morbid obesity are at higher risk for composite neonatal morbidity.


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