Findings vary according to race, ethnicity
A high genetic risk of obesity among pregnant women is linked to fetal weight, but varies according to race, fetal sex, and other factors, according to a study by researchers at the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), part of the National Institutes of Health.
The findings are a step toward understanding how a high maternal genetic risk score for obesity might influence fetal weight. Fetal weight has important implications for health in infancy, childhood, and later in life. The findings suggest that maternal genetic risk scores could one day be used to better understand fetal weight and guide care during pregnancy.
The study was led by Fasil Tekola-Ayele, Ph.D., of NICHD’s Epidemiology Branch. It appears in Obesity.
Fetal growth and weight gain have implications for later health. For example, intrauterine growth restriction, or delayed growth of the fetus, increases the risk of fetal death and birth complications. Similarly, excessive fetal growth, or macrosomia, increases the risk of fetal death and birth and labor complications for both mother and child. Infants of small or large birth size may also face a higher risk of diabetes, obesity, cardiovascular disease, and cancer as adults.
Because maternal weight before and during pregnancy is known to affect fetal growth, the authors sought to learn how a high genetic risk score in pregnant women might influence the growth of their fetuses.
Researchers analyzed records from 2,284 pregnant women who received periodic ultrasound scans as part of the NICHD Fetal Growth Study. The researchers identified 189 genes with variants known to increase the risk of obesity. A woman was considered to have a high genetic risk score for obesity if she had a higher than average number of these variants for her racial and ethnic group.
For Hispanic participants, a high maternal genetic risk score was associated with increased fetal weight at the end of the second and third trimesters. This weight gain was more likely, however, if the mother had a normal weight before pregnancy, had adequate weight gain in the first trimester, or did not gain enough weight in the second trimester.
For Asian participants, a high genetic risk score was associated with increased fetal weight among males, but not females, at the end of the first and second trimesters. For African Americans, a high genetic risk score was associated with nearly triple the risk of being born small for gestational age for male infants. However, for female African American infants, a high genetic risk score was associated with an 80 percent lower risk of being large for gestational age at birth. Infants who are large for gestational age have a higher risk for injury at birth and for childhood obesity.
The authors found no associations between maternal genetic risk scores and fetal weight among white women.
The findings suggest that the genetic risk scores of pregnant women may have implications for understanding fetal weight gain.
Shrestha, D, et al. Maternal BMI-increasing genetic risk score and fetal weights among diverse US ethnic groups. Obesity. 2019. doi:10.1002/oby.22499