National Institutes of Health study finds racial, ethnic differences in fetal growth

CHARLESTON, SC – Current standards for ultrasound evaluation of fetal growth may lead to misclassifying up to 15 percent of minority mothers’ fetuses as being too small, according to a study by researchers at the National Institutes of Health (NIH), the Medical University of South Carolina (MUSC), and other institutions. The study, based on serial scans of more than 1,700 pregnancies, was published online in the American Journal of Obstetrics and Gynecology.

Study authors suggest that many fetuses of minority mothers may be developing normally, but because of hereditary and environmental factors, they are smaller than their white counterparts. The findings could mean that current standards of care recommend that many otherwise healthy, minority pregnant women undergo tests and procedures they don’t need.

Fetal growth restriction is a medical term used to describe fetuses that do not keep up with growth milestones appropriate to their stage of development. Growth restriction is a sign of an underlying health problem, often resulting from the fetus not receiving enough nutrients or oxygen in the uterus.

“We are committed to providing the best in patient care at MUSC, and this often includes looking for those things we could be doing better and with more accuracy,” said study author Roger Newman, M.D., MUSC professor of obstetrics and gynecology and Maas Endowed Chair for Reproductive Sciences. “It’s not in anyone’s best interest to pursue unnecessary testing as I think we all understand that unnecessary testing leads to unnecessary interventions. We are also concerned about the undue stress and worry this places on a mother who is actually progressing just fine but has been told that her baby might not be growing as it should. With the health disparities already present in South Carolina when it comes to pregnancy care, we must make sure that we are aware of the inherent differences in those we serve, and how those differences shape the care they deserve to receive.”

Currently, many practitioners rely on older reference charts for estimating whether a fetus is growing normally. During a sonogram, measurements are taken of the fetus’ head circumference, abdominal circumference and length of the femur (thigh bone). These measurements are used in a formula to estimate the weight of the fetus, which is then compared to a series of estimated weights on a chart of fetal weight stratified by gestational age. The growth chart weights were derived from a study that compiled ultrasound measurements of 139 pregnancies of predominantly middle-class white women during the 1980s.

Current study authors stated new mothers tend to be older, heavier, and more likely to be non-white than when the previous entries were compiled. The researchers sought to compile standards that more accurately reflect the best fetal growth during healthy pregnancies among the most common racial and ethnic groups in the United States. They began by enrolling 2,334 women, aged 18 to 40 years, at 12 hospitals in the United States. The women identified themselves as non-Hispanic white, non-Hispanic black, Hispanic and Asian. The researchers sought only healthy pregnancies so that they could image fetuses whose growth was unaffected by pregnancy-related illness and conditions. Women with such pregnancy-related complications eventually were not included in the standards. More information regarding study specifics is available upon request.

About MUSC

Founded in 1824 in Charleston, The Medical University of South Carolina is the oldest medical school in the South. Today, MUSC continues the tradition of excellence in education, research, and patient care. MUSC educates and trains more than 3,000 students and residents, and has nearly 13,000 employees, including approximately 1,500 faculty members. As the largest non-federal employer in Charleston, the university and its affiliates have collective annual budgets in excess of $2.2 billion. MUSC operates a 750-bed medical center, which includes a nationally recognized Children’s Hospital, the Ashley River Tower (cardiovascular, digestive disease, and surgical oncology), Hollings Cancer Center (one of 68 National Cancer Institute designated centers) Level I Trauma Center and Institute of Psychiatry. For more information on academic information or clinical services, visit musc.edu. For more information on hospital patient services, visit muschealth.org.