Studies examining such phenomena have recently suggested that women having genes related to hypertension risk are more likely to give birth to children with low birth weight.
Researchers, therefore, assumed that mothers with higher systolic blood pressure would have lower-weight newborns. However, no such association was observed.
This caused them to believe that the intrauterine environment plays more of a role in this case. They hypothesized that all of these observations were caused by effects on the placenta.
“We focused on the placenta because it is an extremely vascular organ. Placental weight also frequently correlates with birth weight,” says Noriko Sato, Associate Professor in the Department of Molecular Epidemiology, who led the study.
Genome-wide association studies have shown that many blood pressure-related genes are involved in vascular system development and function.
To examine this further, researchers looked into fetal growth in a cohort of Japanese individuals. They used a person’s genetic risk of developing hypertension over a lifetime, called a polygenic risk score, to know how maternal genetic score influenced placental weight and birth weight.
Then the mediating role of the placenta regarding influence on birth weight was formally verified by the method, called a causal mediation analysis.
They found that nearly 100% of the effect of “vasculature-related” genetic score on birth weight was indeed mediated by placental weight.
They also found an inverse association between maternal systolic blood pressure genetic risk score and the rate of fetal growth towards the end of pregnancy, specifically around 36 weeks of gestation.
These findings suggest that the maternal blood pressure-related genes are associated with undesirable fetal growth deceleration by affecting the placental growth.
Fetal growth restriction in late pregnancy occurs in more than a few percent of pregnancies, and it is mostly of unknown cause and difficult to predict.
However, incorporating maternal genetic risk information into clinical practice could enable screening and improved perinatal management for mother-child health.
Furthermore, the results contribute to the development of new therapeutic targets for the treatment and prevention of hypertension and cardiovascular diseases.