MedicalResearch.com Interview with: Dr. Germaine Louis Buck PhD Senior Investigator and Director of the Division of Epidemiology, Statistics and Prevention Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) National Institutes of Health   Medical Research: What is the background for this study? What are the main findings? Dr. Germaine Buck: We wanted to develop intrauterine standards for ultrasound measured fetal growth, given that none currently exist for contemporary U.S. pregnant women.  Moreover, we wanted to determine if a single standard would be possible for monitoring all pregnant women, or if the standard needed to be tailored to pregnant women’s race/ethnicity.  This added step attempted to address the equivocal data about whether or not race/ethnicity is an important determinant of optimal fetal growth. Analyzing data from 1,737 low risk pregnant women with uncomplicated pregnancies who had 5 ultrasounds done at targeted times during pregnancy, we found significant differences in estimated fetal weight across the 4 maternal race/ethnic groups.  These differences were apparent beginning about 16 weeks gestation and continuing throughout pregnancy.  The differences in these curves were apparent when assessing infant’s birthweight, as well.  Overall, estimated fetal weights while women were pregnant were highest for White mothers followed by Hispanic, Asian, and Black mothers.  A 245 gram difference in estimated fetal weight was observed at 39 weeks gestation between pregnant White and Black women.  This pattern was then observed for measured birth weight, with highest birthweights for White then Hispanic, Asian, and Black infants. Other differences emerged by maternal race/ethnicity for individual fetal measurements:  longest bone (femur & humerus) lengths were observed for Black fetuses emerging at 10 weeks gestation, larger abdominal circumference for White fetuses emerging at 16 weeks gestation, larger head circumference for White fetuses emerging at 21 weeks gestation, and larger biparietal diameter for White fetuses emerging at 27 weeks gestation in comparison to other groups. The race/ethnic differences in fetal size were highly significant and across gestation.  If a single White standard was used for estimating fetal weight for non-White fetuses in pregnant women, between 5% and 15% of their fetuses would have been misclassified as being in the <5th percentile of estimated fetal weight.