Obese women are nearly twice as likely as their lean counterparts to have stillborn babies for several specific, potentially preventable medical reasons, a new University of Pittsburgh Graduate School of Public Health analysis reveals.
Placental diseases and hypertension were the most common causes of stillbirth among obese women, according to the study, published online and scheduled for the October issue of the American Journal of Clinical Nutrition. The research was supported by the National Institutes of Health (NIH).
"We've known for some time that obese women are more likely to have stillbirths, but this is one of the first and most comprehensive efforts to figure out why," said lead author Lisa Bodnar, Ph.D., M.P.H., R.D., associate professor in Pitt Public Health's Department of Epidemiology. "Our hope is that this work can be used to better counsel women on the importance of a healthy pre-pregnancy weight and monitor them for complications during pregnancy that may threaten the survival of their fetuses."
"This study also could be used to guide prevention efforts at a societal level," she said. "If we can reduce pre-pregnancy obesity by even a small amount, through environmental or policy changes, we could significantly reduce the burden of stillbirth."
Annually there are 3.2 million stillbirths worldwide and, of high-income countries, the U.S. is among those with the highest rates. Recent research shows that obesity is likely responsible for more stillbirths in high-income countries than other risk factors, such as smoking or advanced maternal age.
Dr. Bodnar and her colleagues examined records from 658 stillbirths that occurred between 2003 and 2010 at Magee-Womens Hospital of UPMC, which has one of the largest labor and delivery units in the country. Stillbirths were defined as cases where the baby had reached at least 16 weeks gestation and showed no evidence of life after delivery. A panel of obstetricians reviewed each case and assigned a cause of the stillbirth.
The mothers were classified as lean (normal weight or underweight), overweight, obese or severely obese based on their pre-pregnancy body mass index, a measure of weight versus height.
The rate of stillbirth per 1,000 births ranged from 7.7 for lean women to 17.3 for severely obese women.
Maternal hypertension - or high blood pressure in the mother; placental diseases or disorders where the placenta does not properly sustain the unborn baby; fetal abnormalities where the baby would have been unlikely to live if it made it to birth; and umbilical cord abnormalities were all more common in the more obese women.
"Obstetricians should monitor obese patients for these complications and quickly treat conditions like hypertension if they arise in order to reduce risk of stillbirth," said senior author Hyagriv N. Simhan, M.D., professor and chief of the division of maternal-fetal medicine and medical director of obstetrical services at Magee. "However, we'd like to see these women before they even become pregnant. When a doctor has an obese patient who is considering pregnancy, she should be referred to a maternal-fetal medicine specialist who can counsel her on the benefits of losing weight before pregnancy, as well as safe approaches to weight loss."
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