Research

Mother’s genes explain 25% of child’s birth weight

Raskaus
Mother’s genes impact the child’s birth weight even if the child does not inherit the same genes.
Low weight at birth anticipates high blood pressure in adulthood. A recent study shows that this effect is caused by genes instead of environmental factors.

Children inherit half of their genes from their mother and the other half from their father. The genotype that a child receives from his or her parents takes shape to become the child’s unique genetic code. This code, along with environmental factors, impact the child’s birth weight. Among the environmental factors, the most significant one is the mother’s diet during pregnancy.

In a recent study, 190 independent association signals were identified between genetic heredity and birth weight. The study was published in the Nature Genetics magazine.

”In the study, the indirect impact of the mother’s genes on the child’s birthweight was isolated from the impact of the child’s own genes. The birth weight, in turn, is an important indicator of the child’s health later on in life. For example, the mother’s genetic regulation of blood glucose content affected the child’s birth weight,” Professor Terho Lehtimäki explains.

In the study, the genetic inheritance of 230,000 mothers was examined. For each mother, only data for one of her children was included in the research materials. The researchers also used genetic data from 320,000 people and information on their birth weights. The data was acquired from a biobank operating in the United Kingdom and cohorts from the extensive EEG (Early Growth Genetics) consortium.

Terho Lehtimäki kasvokuva
Terho Lehtimäki says that the onset of various diseases in adulthood may be anticipated from birth weight.

Mother’s glucose values steer the child’s growth

The study revealed that approximately 25% of the genetic factors impacting a child’s birth weight came from the mother’s side. The child did not inherit these genes, but instead their impact on the baby’s growth manifested itself through the growth environment during pregnancy. One of the affecting factors was the amount of available glucose.

”The glucose produced by the mother’s body is a key factor in fetal growth. The glucose runs through the placenta and increases insulin production in the fetus’s body. An expecting mother’s elevated fasting sugar value predicts a higher weight for the child to be born,” Lehtimäki states.

In some cases, the mother’s and child’s genes cooperate and steer the child’s birth weight into the same direction. Other genes, in turn, try to steer the development into other directions. One example of the combined impact of the mother’s and child’s genetics has to do with the mother’s glucose values.

If the mother’s genetics aims to raise the body’s glucose values during pregnancy, the child grows to be bigger, since the child’s own genetic code starts to produce more insulin. The opposite will happen when the child inherits the same insulin production-related genes from his or her mother. In this event, the child’s heredity limits the amount of insulin in his or her body. In other words, even if the mother’s genetics steers the child to grow bigger, the child’s own genetic code fights back.

”Alleles, which increase insulin production in the mother’s body, also lower the mother’s glucose values. This phenomenon, in turn, reduces insulin production in the fetus’s body,” Lehtimäki says.

Birth weight is an important research subject

Previous studies have shown that a birth weight below normal increases the risk of labour complications. Furthermore, a low weight at birth increases the risk of high blood pressure in adulthood. The newly published study revealed that the risk of higher blood pressure as an adult is due to genetic factors instead of environmental factors during pregnancy.

Both exceptionally low and high birth weights increase the risk of labour mortality. They also raise the individual’s risk of metabolic disorder onset at a later age.

”The impact of genes on birth weight is an important research subject since birth weight has been found to have major importance in the development of diabetes, high blood pressure and heart and vascular diseases,” Lehtimäki notes.

Text: Jaakko Kinnunen
Photos: Jonne Renvall

Maternal and fetal genetic effects on birth weight and their relevance to cardio-metabolic risk factors