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Study finds racial, ethnic differences effect fetal growth

Significant size differences in completely healthy fetuses were ascribed by researchers to environmental or hereditary causes.

By Stephen Feller
Study finds racial, ethnic differences effect fetal growth
A National Institutes of Health study found that minority women often have fetuses that are healthy and developing normally, but are smaller than growth milestones which are largely based on white women's pregnancies. Photo by Monkey Business Images/Shutterstock

BETHESDA, Md., Sept. 29 (UPI) -- Some pregnant minority women who are otherwise healthy may be exposed to unnecessary tests and procedures because of incorrect concerns that their fetuses are smaller than statistically expected, according to a new study.

It can be difficult to tell the difference between a growth restricted fetus and a healthy one, similar to children who are healthy but small for their age, researchers said. The new study, funded by the National Institutes of Health, found that environmental and hereditary factors can result in sometimes smaller, but still healthy, fetuses of minority mothers.

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Fetal growth restriction, the medical term for fetuses not meeting standard growth milestones, often indicates other health issues such as a fetus not receiving enough nutrients or oxygen in the uterus.

"Doctors like to be proactive -- if they suspect there's a problem with a fetus' growth, then they're likely going to order tests and investigate," said Dr. Germaine Buck Louis, Director of the Division of Intramural Population Health Research at the National Institute of Child Health and Human Development, in a press release. "But inaccurate standards may be leading women to receive unnecessary tests -- not to mention the stress of thinking something may be wrong -- when their pregnancies actually are on track."

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Researchers recruited 2,334 healthy women with low-risk pregnancies from 12 medical centers between 2009 and 2013, of which 614 were non-Hispanic whites, 611 were non-Hispanic blacks, 649 were Hispanic, and 460 were Asian.

The women were screened between weeks 8 and 13 of their pregnancies for maternal health status that presumes healthy fetal growth. The criteria includes the women being aged between 18 and 40, having a body mass index between 19.0 and 29.9 kg, maintaining healthy lifestyles and living conditions, and having a low-risk medical and obstetrical history.

After evaluating the women, 1,737 women remained in the study with healthy pregnancies, who were then assigned to one of four groups and scheduled for a series of five sonograms at intervals that ranged from the 16th to the 41st week of pregnancy.

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From the 20th week of pregnancy on, the researchers reported seeing significant weight differences in the fetuses. By the 39th week -- nearing full-term pregnancy -- the researchers found the average weights of fetuses for white mothers was 4,402 grams, for Hispanic mothers was 4,226 and for black mothers was 4,053.

Over the course of the study, the researchers found that 5 to 15 percent of minority fetuses were below the 5th percentile for fetal weight based on the white standard. At 35 weeks, 14 percent of black mothers and 15 percent of Asian mothers fetuses would be considered below the 5th percentile.

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The standard growth charts now in use were derived from a study in the mid-1980s with middle-class white women. Mothers today, researchers wrote in the new study, tend to be older, heavier and more likely to be non-white -- so the inconsistencies between the charts and reality for healthy fetuses are not entirely shocking.

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Researchers concluded in the study that standards should be adjusted, or additional ones created, that include racial and ethnic differences based on the significant differences between the four groups of women's fetuses.

The study is published in the American Journal of Obstetrics and Gynecology.

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