Standards for fetal growth complicated by normal racial variations

SAN DIEGO – Fetal growth rates vary significantly among racial and ethnic groups, according to findings from a prospective cohort study.

The findings, which suggest that a single standard is not appropriate for all population subgroups, have implications for the development of fetal growth standards in the United States, Dr. Katherine Laughon Grantz reported at the annual Pregnancy Meeting sponsored by the Society for Maternal-Fetal Medicine.

“There is potential for significant misclassification if standards are used that are based on either one race or that use a pooled racial ethnic group, and a single standard is not appropriate for fetal growth in contemporary U.S. obstetrical calculations,” she said.

Of 2,334 healthy women with low-risk singleton pregnancies who participated in the trial – a National Institute of Child Health and Human Development (NICHD) growth study – 26% were Caucasian, 26% were African American, 28% were Hispanic, and 20% were Asian. After exclusion of those who developed pregnancy complications or were lost to follow-up, 1,737 remained.

The growth curves began to differ between the groups beginning at 16 weeks gestation, and extended to delivery, said Dr. Grantz of the NICHD in Rockville, Md.

After 20 weeks’ gestation, highly significant differences were seen between the groups in estimated fetal weight. At 35 weeks’ gestation, the 10th, 50th, and 90th estimated fetal weight percentiles were 2,305 g, 2,727 g, and 3,227 g for Caucasians; 2,179 g, 2,607 g, and 3,121 g for Hispanics; 2,140 g, 2,530 g, and 2,987 g for Asians; and 2,140 g, 2,528 g, and 2,987 g for African Americans.

Differences in abdominal circumference paralleled the differences in estimated fetal weight, Dr. Grantz said.

After 25 weeks’ gestation, statistically significant differences in head circumference emerged, and at 35 weeks, median head circumference was 320 cm in Caucasians, 317 cm in Hispanics, 316 cm in Asians, and 314 cm in African Americans, she said.

Other differences included humerus and femur length, which were longer throughout gestation in African Americans than in the other racial/ethnic groups – similar to adult proportions.

The women were recruited between 2010 and 2013 from 12 clinical sites. They were screened between 8 weeks and 13 weeks plus 6 days for low-risk status associated with optimal fetal growth. The women were then randomized to one of four serial 2D/3D ultrasonology schedules with quality assurance for longitudinal fetal measurements. This approach was taken to allow for adequate representation of each gestational week without subjecting the women to too many ultrasounds, Dr. Grantz said.

The differences remained statistically significant after adjustment for various demographic differences between the groups.

“Optimal fetal growth is the foundation of long-term health,” Dr. Grantz said, noting that despite this understanding, identifying normal fetal growth remains a pressing challenge.

The current findings suggest that fetuses growing in optimal conditions, with normal maternal size and normal pregnancy outcomes, differ in proportion and size by race/ethnicity, she said.

Dr. Grantz is an employee of the NICHD, which supported the study.

SAN DIEGO – Fetal growth rates vary significantly among racial and ethnic groups, according to findings from a prospective cohort study.

The findings, which suggest that a single standard is not appropriate for all population subgroups, have implications for the development of fetal growth standards in the United States, Dr. Katherine Laughon Grantz reported at the annual Pregnancy Meeting sponsored by the Society for Maternal-Fetal Medicine.

“There is potential for significant misclassification if standards are used that are based on either one race or that use a pooled racial ethnic group, and a single standard is not appropriate for fetal growth in contemporary U.S. obstetrical calculations,” she said.

Of 2,334 healthy women with low-risk singleton pregnancies who participated in the trial – a National Institute of Child Health and Human Development (NICHD) growth study – 26% were Caucasian, 26% were African American, 28% were Hispanic, and 20% were Asian. After exclusion of those who developed pregnancy complications or were lost to follow-up, 1,737 remained.

The growth curves began to differ between the groups beginning at 16 weeks gestation, and extended to delivery, said Dr. Grantz of the NICHD in Rockville, Md.

After 20 weeks’ gestation, highly significant differences were seen between the groups in estimated fetal weight. At 35 weeks’ gestation, the 10th, 50th, and 90th estimated fetal weight percentiles were 2,305 g, 2,727 g, and 3,227 g for Caucasians; 2,179 g, 2,607 g, and 3,121 g for Hispanics; 2,140 g, 2,530 g, and 2,987 g for Asians; and 2,140 g, 2,528 g, and 2,987 g for African Americans.

Differences in abdominal circumference paralleled the differences in estimated fetal weight, Dr. Grantz said.

After 25 weeks’ gestation, statistically significant differences in head circumference emerged, and at 35 weeks, median head circumference was 320 cm in Caucasians, 317 cm in Hispanics, 316 cm in Asians, and 314 cm in African Americans, she said.

Other differences included humerus and femur length, which were longer throughout gestation in African Americans than in the other racial/ethnic groups – similar to adult proportions.

The women were recruited between 2010 and 2013 from 12 clinical sites. They were screened between 8 weeks and 13 weeks plus 6 days for low-risk status associated with optimal fetal growth. The women were then randomized to one of four serial 2D/3D ultrasonology schedules with quality assurance for longitudinal fetal measurements. This approach was taken to allow for adequate representation of each gestational week without subjecting the women to too many ultrasounds, Dr. Grantz said.

The differences remained statistically significant after adjustment for various demographic differences between the groups.

“Optimal fetal growth is the foundation of long-term health,” Dr. Grantz said, noting that despite this understanding, identifying normal fetal growth remains a pressing challenge.

The current findings suggest that fetuses growing in optimal conditions, with normal maternal size and normal pregnancy outcomes, differ in proportion and size by race/ethnicity, she said.

Dr. Grantz is an employee of the NICHD, which supported the study.

SAN DIEGO – Fetal growth rates vary significantly among racial and ethnic groups, according to findings from a prospective cohort study.

The findings, which suggest that a single standard is not appropriate for all population subgroups, have implications for the development of fetal growth standards in the United States, Dr. Katherine Laughon Grantz reported at the annual Pregnancy Meeting sponsored by the Society for Maternal-Fetal Medicine.

“There is potential for significant misclassification if standards are used that are based on either one race or that use a pooled racial ethnic group, and a single standard is not appropriate for fetal growth in contemporary U.S. obstetrical calculations,” she said.

Of 2,334 healthy women with low-risk singleton pregnancies who participated in the trial – a National Institute of Child Health and Human Development (NICHD) growth study – 26% were Caucasian, 26% were African American, 28% were Hispanic, and 20% were Asian. After exclusion of those who developed pregnancy complications or were lost to follow-up, 1,737 remained.

The growth curves began to differ between the groups beginning at 16 weeks gestation, and extended to delivery, said Dr. Grantz of the NICHD in Rockville, Md.

After 20 weeks’ gestation, highly significant differences were seen between the groups in estimated fetal weight. At 35 weeks’ gestation, the 10th, 50th, and 90th estimated fetal weight percentiles were 2,305 g, 2,727 g, and 3,227 g for Caucasians; 2,179 g, 2,607 g, and 3,121 g for Hispanics; 2,140 g, 2,530 g, and 2,987 g for Asians; and 2,140 g, 2,528 g, and 2,987 g for African Americans.

Differences in abdominal circumference paralleled the differences in estimated fetal weight, Dr. Grantz said.

After 25 weeks’ gestation, statistically significant differences in head circumference emerged, and at 35 weeks, median head circumference was 320 cm in Caucasians, 317 cm in Hispanics, 316 cm in Asians, and 314 cm in African Americans, she said.

Other differences included humerus and femur length, which were longer throughout gestation in African Americans than in the other racial/ethnic groups – similar to adult proportions.

The women were recruited between 2010 and 2013 from 12 clinical sites. They were screened between 8 weeks and 13 weeks plus 6 days for low-risk status associated with optimal fetal growth. The women were then randomized to one of four serial 2D/3D ultrasonology schedules with quality assurance for longitudinal fetal measurements. This approach was taken to allow for adequate representation of each gestational week without subjecting the women to too many ultrasounds, Dr. Grantz said.

The differences remained statistically significant after adjustment for various demographic differences between the groups.

“Optimal fetal growth is the foundation of long-term health,” Dr. Grantz said, noting that despite this understanding, identifying normal fetal growth remains a pressing challenge.

The current findings suggest that fetuses growing in optimal conditions, with normal maternal size and normal pregnancy outcomes, differ in proportion and size by race/ethnicity, she said.

Dr. Grantz is an employee of the NICHD, which supported the study.