Research evaluates neonatal outcomes of pregnancies complicated by maternal obesity

Obesity is linked to many adverse health outcomes, including pregnancy. However, little is known about the effect of maternal obesity on neonatal mortality and morbidity.

A study recently published in American Journal of Obstetrics and Gynecology Maternal-Fetal Medicine Discusses the relationship of maternal body mass index (BMI) in 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 in pregnancy is relatively common, with approximately one-third of pregnancies in the United States complicated by obesity. Obesity is linked to maternal hypertension, diabetes, and pre-eclampsia, as it is a chronic inflammatory condition.

During pregnancy, obese mothers are more likely to have miscarriages and stillbirths, infants born to these mothers are at greater risk of congenital anomalies, macrosomia, shoulder dystocia, neonatal death and meconium aspiration.

The current study examines how maternal obesity affects newborn health and mortality. Here, scientists used data from a set of singleton deliveries from 24-42 weeks’ gestation at 25 hospitals between 2008-2011.

Maternal BMI was categorized into reference groups of normal/overweight. The experimental groups of obese (OB), morbidly obese (MO), and super-morbidly obese (SMO) were classified based on BMI, with values ​​ranging from 30–39.9 kg/m.240-49.9 kg/m2and 50 kg/m2 or more, respectively. Reference BMI values ​​ranged from 18.5-29.9 kg/m2.

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

The scientists evaluated neonatal death, hypoxic-ischemic encephalopathy (HIE), respiratory distress syndrome, and other neonatal complications. Preterm delivery, defined as birth before 37 weeks of gestation, was also included, as well as maternal pre-eclampsia and eclampsia.

What did the study show?

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, increasing with BMI, although at a lower rate than in the reference group.

Hispanics were overrepresented in the OB group, while black mothers were overrepresented in the MO and SMO groups, with a higher proportion of women with a history of cesarean section. Pre-eclampsia, eclampsia and cesarean section were reported more frequently due to increased BMI.

Preterm birth was less likely in the OB group but increased from OB to SMO at less than 37 weeks and less than 28 weeks of gestation. Birth weight increases with maternal BMI, with increased odds of a baby weighing more than 4 kg during pregnancy among OB, MO, and SMO mothers. These babies were also more likely to have birth defects.

Newborns born to MO mothers had a one-third increased risk of neonatal morbidity compared to those born to women in the reference group. However, no such association was shown for children 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 effects?

Even after allowing for the confounding effects of maternal diabetes, pre-eclampsia, and preterm delivery, infants born to MO mothers had more severe neonatal morbidities than infants in the reference group.

However, neonatal mortality did not increase according to maternal BMI. Furthermore, composite morbidity in newborns did not increase with increasing BMI, if the presence of chronic hypertension and pre-existing diabetes were accounted for.

Children born to MO and SMO mothers are more likely to weigh more than 4 kg and have birth defects, confirming previous reports. However, there is some controversy about the validity of this finding, although preterm delivery appears to be more common among babies born to already obese mothers, with the current study reporting fewer preterm births among OB mothers. Conversely, increasing BMI increased the risk of delivering at less than 37 weeks and at less than 28 weeks.

The reasons for the increased short-term neonatal morbidity in children born to obese mothers remain to be identified; However, normalizing BMI before conception can help prevent or reduce the adverse effects of obesity in newborns, as well as controlling chronic hypertension and diabetes.

Journal Reference:

  • Dinsmoor, MJ, Hill, 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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