A high genetic risk for obesity in Hispanic mothers is associated with increased fetal weight throughout pregnancy, according to new research in the U.S. The data also showed that, depending on the sex of the offspring, this risk had a different effect on fetal and birth weights in Black and Asian populations.
The study, “Maternal BMI‐Increasing Genetic Risk Score and Fetal Weights among Diverse US Ethnic Groups,” was published in the journal Obesity.
Common genetic changes are associated with variations in body mass index (BMI). Genetic risk scores aggregate data from multiple single nucleotide polymorphisms (SNPs), which are differences in a single nucleotide, the building blocks of DNA. These risk scores have helped to classify individuals into high or low genetic risk groups.
Maternal genetic risk for obesity plays a role in the link between maternal obesity before pregnancy and offspring birth weight. Both maternal pre-pregnancy BMI and gestational weight gain (GWG) are associated with fetal growth.
The investigators addressed the lack of information about the relationship between maternal BMI, genetic risk score (GRS), and fetal growth at clinically relevant gestation windows. Their research included 189 SNPs and focused on fetal weight the end of the first trimester of pregnancy (13 weeks and six days), the end of the second trimester (27 weeks and six days), and the end of the third trimester (40 weeks).
Four race/ethnic groups of women were recruited from 12 clinical sites in the U.S. between July 2009 and January 2013. Among the 1,945 participants, 603 were white, 591 were black, 535 were Hispanic, and 216 were Asian.
The scientists also analyzed the odds for small‐for‐gestational age (SGA), which is birth weight lower than the 10th percentile, and large‐for‐gestational age (LGA), which is birth weight greater than or equal to the 90th percentile. Additionally, they assessed whether differences in pre-pregnancy BMI, GWG, and fetal sex influenced the results. Fetal weight was calculated via ultrasound measurement of fetal head circumference, abdominal circumference, and femur (a hindlimb bone) length.
In Hispanic women only, having a high GRS that’s above the median value significantly correlated with increased fetal weight at the end of the second and third trimesters. The effect of GRS was greater in Hispanic women with normal pre-pregnancy weight, an adequate first trimester GWG, or an inadequate second trimester GWG.
Additionally, a high GRS in Asian women was associated with increased weight in male fetuses but decreased weight in female fetuses.
The data also showed that, in black offspring, having a mother with high GRS was significantly associated with a 2.6‐fold greater likelihood of SGA among males and an 80% lower risk of LGA among females.
“Our findings suggest that the genetic risk of pregnant mothers is potentially informative to understanding variations in fetal weight,” the researchers wrote.