Thanks to outdated standards for ultrasound evaluations, up to 15 percent of multicultural mothers are misjudged as carrying fetuses that are too small. The miscalculation frequently leads to countless women of color being subjected to unnecessary testing and procedures during their otherwise healthy pregnancies.

The fetuses of many multicultural women are developing normally, despite being smaller than their white counterpart. Nonetheless, a study published today by the National Institutes of Health (NIH) has found that existing standards for ultrasound evaluation misclassify up to 15 percent of fetuses belonging to multicultural mothers as being too small.

The term "fetal growth restriction" refers to fetuses that fail to meet growth milestones that are appropriate for their stage of development. The growth delay could be an indicator of underlying health issues, which often results in the fetus not receiving enough oxygen or nutrients in the uterus.

The NIH report clarified that hereditary and environmental factors often cause these otherwise healthy fetuses to develop smaller. The findings showed that many healthy women are subjected to unnecessary tests and procedures because of misclassifications.  

"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 the study's first author, Germaine Buck Louis, Ph.D, Director of the Division of Intramural Population Health Research at NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), 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."

The American Journal of Obstetrics and Gynecology published the study, which was based on serial scans of more than 1,700 pregnancies. The ultrasonic examination, whereby sound waves are used to create an image of the maturing fetus, was used to detect issues in pregnancy, problems with fetal heart or placenta and to determine if the fetus was developing too slowly. The slowed growth can point to a condition referred to as fetal, or intrauterine, growth restriction, and it could potentially signify fetal heart diseases, the placenta's failure to deliver enough blood or maternal high blood pressure. Growth-restricted infants also face added risk of diabetes, heart disease and death. Nonetheless, growth restrictions can sometimes be indistinguishable from fetuses that are growing normally.

Unfortunately, many healthcare practitioners still rely on older reference charts when estimating normal fetus growth. They use measurements from a fetus' head circumference, abdominal circumference and length of the femur (thigh bone) to estimate the weight of the fetus, which is then compared to a chart of fetal weight stratified by gestational age. That chart is derived from a study conducted by Frank Hadlock and his colleagues, who held a small-scale study that predominately featured middle-class white women during the 1980s.

NIH researchers compiled standards that more accurately reflect the fetal growth during healthy pregnancies among multiethnic groups. They conducted research at 12 hospitals in the United States and enrolled 1,700 women with healthy pregnancies, aged 18 to 40 years. They gauged fetus growth and they found that by the 39th week, fetuses of white mothers were the largest at 4402 grams, followed by fetuses of Hispanic mothers (4226 grams). Fetuses of black mothers were the smallest at 4053 grams. The figures prove that fetuses born to non-white mothers tend to be smaller, which would suggest a need for renewed efforts to detect fetal growth abnormalities.

According to the report, it should be taken into consideration that women today are more likely to have children at an older age, women tend to heavier and new mothers are more likely to be a non-white. The study authors believe that future studies should determine new fetal growth standards, and future standards should attempt to take racial and ethnic differences into account.