Stillbirth More Common for Mothers With Obesity

Obesity may pose a significant threat to healthy pregnancies, according to a mediation analysis.

In a study of 392,820 women, those who had obesity prior to pregnancy had 55% higher odds of perinatal mortality — defined as stillbirth or neonatal death before hospital discharge (adjusted OR 1.55, 95% CI 1.36-1.77), reported Jeffrey Bone, a PhD candidate at the University of British Columbia in Vancouver, and colleagues.

Even women who were just overweight prior to pregnancy saw 22% higher odds of perinatal mortality compared with woman who had a normal BMI (aOR 1.22, 95% CI 1.08-1.37), the group reported in PLoS One.

The biggest driving force between these two factors was gestational age at delivery, mediating 63.1% of the association between obesity and perinatal death, the researchers reported.

These associations were adjusted for chronic hypertension, smoking, substance and alcohol use, prior stillbirth, prior preterm birth, parity, maternal age, year of birth, chronic diseases, and asthma.

“[Women with obesity] tend to experience worse pregnancy outcomes, including higher rates of neonatal death and stillbirth, but the reasons for this are not fully understood,” Bone told MedPage Today. “We wanted to see if some of this could be explained by their pregnancies ending earlier than women with normal weight.”

However, while these findings didn’t come as much of a surprise, he said there are still many remaining questions left to explore. In particular, the group suggested future research parse out which potential precursors leading to a higher pre-pregnancy BMI may have the greatest effect on perinatal mortality, such as a sedentary lifestyle, high calorie food intake, and medical or genetic conditions.

Regardless, the study should highlight the need for special attention to pregnant women with obesity in order to prevent stillbirth and neonatal death, especially in the second trimester.

“[Healthcare providers should keep in mind] that the reasons for increased risks are complex, including maternal complications leading to preterm birth that occur more frequently in obese women, as well as fetal and placental reasons,” Bone added. “More studies, and more detailed analyses such as these, will be needed to better target interventions to women with high pre-pregnancy BMI.”

The researchers assessed data on 547,401 singleton live births and stillbirths that occurred in British Columbia from 2004 to 2017. Data were excluded for late terminations and women with births prior to 20 weeks gestation.

Among 392,820 women, 50,352 (12.8%) had obesity, 81,065 (20.6%) were overweight, 237,726 (60.6%) were normal weight, and 23,677 (6.0%) were underweight. These pre-pregnancy weights were self-reported and abided by the following BMI categories: underweight (<18.5), normal (18.5 to <25), overweight (25 to <30), and obesity (BMI 30+).

Compared with women who had a normal BMI, women with obesity were more likely to be multiparous, smoke during their pregnancy, have chronic and gestational hypertension or diabetes, and have a prior caesarean delivery.

As for preterm birth rates, they followed a gradient as BMI increased: 7.3% among women with a normal BMI, 8.1% for overweight women, and 9.7% for women with obesity, the researchers said.