Research evaluates neonatal outcomes of pregnancies complicated by maternal obesity


Obesity is associated with many adverse health consequences, including during pregnancy. However, there is little information on the effect of maternal obesity on neonatal mortality and morbidity.

A recent study published in the American Journal of Obstetrics & Gynecology Maternal-Fetal Medicine discusses the association of maternal body mass index (BMI) during pregnancy with neonatal outcomes. More specifically, the researchers were interested in determining whether maternal obesity increased the risk of poor neonatal outcomes, independent of the presence of pre-existing diabetes and chronic hypertension.

Study: Short-term neonatal outcomes of pregnancies complicated by maternal obesity. Image credit: FotoDuets /


Maternal obesity is relatively common during pregnancy, with about one-third of pregnancies in the United States complicated by obesity. Obesity is associated with maternal hypertension, diabetes and preeclampsia as it is a chronic inflammatory condition.

During pregnancy, obese mothers are more likely to experience miscarriage and stillbirth, with these mothers’ babies being at greater risk for congenital anomalies, macrosomia, shoulder dystocia, neonatal death, and meconium aspiration.

The current study examines how maternal obesity affects neonatal health and mortality. In this, the scientists used data from a series of singleton deliveries from 24-42 weeks gestation in 25 hospitals between 2008-2011.

The mother’s BMI was assigned to the normal/overweight reference group. The experimental groups of obesity (OB), morbid obesity (MO), and supermorbid obesity (SMO) were categorized by BMI, with values ​​ranging from 30-39.9 kg/m240-49.9 kg/m²2and 50 kg/m2 or more, respectively. Reference BMI values ​​were between 18.5-29.9 kg/m2.

All patients in the reference and other groups were matched on baseline characteristics such as age, race, ethnicity, chronic hypertension, diabetes and previous cesarean delivery, along with cigarette use and insurance status.

The scientists assessed neonatal mortality, hypoxic-ischemic encephalopathy (HIE), respiratory distress syndrome and other neonatal complications. Preterm birth, defined as birth before 37 weeks gestation, as well as maternal preeclampsia and eclampsia, were also included.

What did the research reveal?

The current study included more than 52,000 patients and their newborns, of whom 42% were OB and 7% and 1% were MO and SMO, respectively. Obesity was associated with pre-existing diabetes, chronic hypertension and cigarette use, and increased with BMI, although at a slower rate compared to the reference group.

Hispanics were overrepresented in the OB group, while black mothers were overrepresented in the MO and SMO groups, which also had a higher percentage of women with a history of cesarean delivery. Preeclampsia, eclampsia and caesarean section were reported more frequently as BMI increased.

Preterm births were least likely in the OB group, but increased from OB to SMO at less than 37 weeks and less than 28 weeks gestation. Birth weights tended to increase with maternal BMI, with infant weights greater than 4 kg being more likely during pregnancies in OB, MO, and SMO mothers. These babies were also more likely to have a birth defect.

The risk of neonatal morbidity increased by a third in newborns born to MO mothers compared to those born to women in the reference group. However, no such association was observed for infants born to OB or SMO mothers. Pre-existing obesity and obesity in early pregnancy may predict an increased risk of more significant neonatal morbidity.

What are the implications?

Severe neonatal disease was higher for infants born to MO mothers compared to those in the reference group, even after accounting for the confounding effects of maternal diabetes, preeclampsia, and preterm birth.

However, neonatal mortality did not increase in line with maternal BMI. In addition, compound morbidity among neonates did not increase with increasing BMI, provided the presence of chronic hypertension and pre-existing diabetes was taken into account.

Babies born to MO and SMO mothers weigh more than 4 kg and have congenital disabilities, confirming previous reports. While preterm birth has previously been observed to be more common in babies born to obese mothers, there is some controversy over the validity of this finding, with the current study reporting fewer preterm births in OB mothers. Conversely, the risk of preterm birth at less than 37 weeks and less than 28 weeks increased with increasing BMI.

The reasons underlying the increased near-term neonatal morbidity in babies born to obese mothers have yet to be identified; however, normalizing BMI before conception, in addition to controlling chronic hypertension and diabetes, may help prevent or reduce the adverse impact of obesity on neonatal outcomes.

Magazine reference:

  • Dinsmoor, MJ, Ugwu, LG, Bailit, JL, et al. (2023). Short-term neonatal outcomes of pregnancies complicated by maternal obesity. American Journal of Obstetrics and Gynecology. doi:10.1016/j.ajogmf.2023.100874.
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