Study: Obesity a risk factor for stillbirth, especially at term

Obesity is a risk factor for stillbirth, and the risk increases as pregnancy advances to term, according to a large study published in CMAJ (Canadian Medical Association Journal).

The overall risk of stillbirth in pregnancy is approximately 0.4% in Canada. "Our findings suggest that an earlier delivery date may help reduce the risk of stillbirth for pregnant people with obesity," says lead author Dr. Naila Ramji, a high-risk pregnancy specialist in Fredericton, New Brunswick, and assistant professor at Dalhousie University, with co-authors at The Ottawa Hospital and senior author Dr. Laura Gaudet, a high-risk pregnancy specialist and associate professor at Queen's University.

Although the link between obesity and stillbirth is well-known, there was little research on the association between obesity and stillbirth risk by gestational age or on the impact of higher classes of obesity.

To address this gap, the researchers analyzed data from the Better Outcomes Registry and Network on 681 178 singleton births, 1956 of which were stillbirths, in Ontario between 2012 and 2018. After adjusting for other stillbirth risk factors like diabetes and high blood pressure, the researchers found that people with class I obesity (BMI 30–34.9 kg/m²) had double the risk of stillbirth at 39 weeks gestation compared to those with normal BMI (18.5–24.9 kg/m²).

For those in obesity classes II and III (BMI 35–39.9 kg/m² and BMI 40 kg/m² and higher, respectively), stillbirth risk at 36 weeks was 2 to 2.5 times that of people with normal BMI. This risk further increased with gestational age, with a more than fourfold risk at 40 weeks.

"For other medical conditions that increase the risk of stillbirth, there are guidelines that recommend delivery at 38 or 39 weeks. Interestingly, the risk thresholds for those conditions are lower than the risks we found associated with obesity. We worry that implicit biases against people with obesity may be causing the medical community to take the risks they face less seriously," says Dr. Ramji.

The authors also looked at whether stillbirths occurred before or during delivery and found a higher risk of stillbirths occurring before delivery in people with class I and II obesity.

They hope that these findings will improve care for this at-risk population.

"Pregnant people with obesity, especially those with additional risk factors, may benefit from timely referral and greater surveillance closer to term, and the presence of additional risk factors may warrant earlier delivery," says Dr. Ramji.

In a related editorial, CMAJ editor Dr. Naomi Cahill urges that health care providers take a nuanced approach in prenatal counseling of patients with obesity.

"Focusing on weight during communications of risk may reinforce weight bias, weight stigma, and discrimination for pregnant people," writes Dr. Cahill, a registered dietitian.

"Negative weight-related attitudes, beliefs, assumptions, and judgments prevalent in society, and harmful social stereotypes that are held about people living with obesity are associated with adverse physical and mental health consequences." She ends by saying that pregnant people living with obesity "… should receive respectful prenatal care, free from stigma, that realizes the goals of both health care providers and patients to ensure positive maternal and fetal outcomes."