Maternal Obesity May Account for 25% of Late Stillbirths

Veronica Hackethal, MD

March 27, 2014

Updated April 9, 2014.

Nearly 1 in 4 stillbirths may be linked to maternal obesity, with the risk even higher as gestational age and obesity levels increase, according to a large population-based study published online March 27 in the American Journal of Obstetrics & Gynecology.

"There is a pronounced increase in the risk of stillbirth with increasing [body mass index (BMI)]," Ruofan Yao, MD, MPH, from the Department of Obstetrics and Gynecology, Drexel University College of Medicine, Philadelphia, Pennsylvania, and colleagues write.

They add, "These findings, if reproduced, would make obesity the single most important risk factor for stillbirth in the general population."

Obesity during pregnancy is linked to gestational diabetes, hypertension, thromboembolism, preeclampsia, delayed labor, increased caesarean, and stillbirth, according to the authors.

To determine whether it is also linked to stillbirth, the authors analyzed vital records databases for stillbirths and singleton live births without severe fetal anomalies between 20 and 42 weeks' gestation in Texas from 2006 to 2011 and Washington from 2003 to 2011. Gestational age was divided into 4 groups, and BMI was categorized according to World Health Organization recommendations. The authors adjusted their analyses for maternal age, primiparity, education, no prenatal care, race/ethnicity, smoking status, chronic hypertension, and pregestational diabetes.

They identified 2,868,482 singleton births in the records, including 9030 stillbirths. The risk for stillbirth increased with increasing maternal weight compared with normal-weight women (hazard ratio, 1.36 with overweight; 1.71 with class 1 obesity, 2.00 with class 2 obesity, 2.48 with class 3 obesity, and 3.16 for women with a BMI at or above 50 kg/m2).

Approximately 25% of the stillbirths that occurred between gestational weeks 37 and 42 were attributable to maternal obesity. For each gestational age category, as BMI increased, so did the risk for stillbirth. Stillbirth risk escalated more sharply near the end of pregnancy for women with higher BMIs. Compared with normal-weight women, having a BMI of 50 kg/m2 or higher was associated with a 5.7 times greater risk for stillbirth at 39 weeks' gestation and a 13.6 times greater risk at 41 weeks' gestation.

The study was confined by differences between the 2 data sets and was subject to limitations inherent in large population databases. About 30% of stillbirths were excluded from the analysis because of missing data, which may have lead to underestimation of obesity-related stillbirth risk. Generalizability may also be an issue, as data came from only 2 states. Inaccuracies in estimating the exact time of fetal death, which could occur earlier than stillbirth diagnosis, could shift results to earlier gestational ages. Finally, prepregnancy weight was self-reported and could have been underestimated, which could, in turn, underestimate the risk for stillbirth by BMI category.

The authors emphasize that perinatal deaths began to increase at 41 weeks for most women but sharply increased at 39 weeks for women with BMIs of 50 kg/m2 or higher. This pattern could be explained, according to the authors, by earlier fetal growth velocity and earlier uteroplacental insufficiency among obese women. They note that these results support the current practice of delivering babies by 41 weeks and suggest that fetal surveillance could be useful among obese pregnant women.

"Although the findings as reported here are significant, especially for the most obese women...[the] magnitude of the risk actually may be underestimated," the authors caution. "[T]his particular group has significantly higher comorbidities that, by themselves, would warrant frequent fetal testing and a tendency toward earlier delivery."

The authors have disclosed no relevant financial relationships.

Am J Obstet Gynecol. Published online March 27, 2014. Abstract

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