Excess weight in mothers-to-be may cause the birth of sons with high chances of low fertility in the future, according to a new study. The research conducted by Denmark researchers also found that the outcome wasn’t similar for daughters as their fertility levels seemed to be unaffected. 

In recent times, there have been records of a decline in the fertility rate globally. Infertility has resulted in struggles in some couples trying to conceive naturally. Previous studies suggest most impacts on a child’s metabolic and cardiovascular system are tied to cases of infertility.

To begin with, this is the first study on the outcome of overweight or obesity during pregnancy on the fertility of sons and daughters. The study authors worked to explore if a mother’s body weight when pregnant was tied to the chances of infertility in adult sons and daughters. On a larger scale, the study authors considered factors such as health, lifestyle, and sociodemographic factors of the women during pregnancy. 

Researchers from Aarhus University in Denmark looked at data of over 9232 children of pregnant women enrolled in the hospital at the 36th gestational week. Of which 4730 were sons while the other 4502 were daughters. To estimate Body Mass Index, they collected data on the mother’s weight and height when trying to get pregnant, along with her current weight at the time of the visit.

The mothers were then grouped into underweight, normal weight, and overweight according to the WHO criteria. Over 10 percent of children were born to underweight mothers. Likewise, 77 percent and 13 percent of children were born to normal and overweight mothers respectively.

Due to the low rate of obese mothers at the time of the study, the authors couldn’t account for obese mothers and overweight mothers separately. So they joined both groups to create a “maternal overweight ” group, recording a BMI greater than 25kg/m².

The study participants were followed up to 34 years post-birth with researchers noting that about 9.4 percent of the sons had low sperm counts indicating infertility.

From the result, they found that compared to sons of normal-weight mothers, overweight mothers with a BMI greater than 25kg/m² increased their son’s likelihood of infertility. On the other hand, sons of mothers classified as underweight did not present with chances of infertility. Surprisingly though, the researchers found that daughters fertility seemed to be unaffected by changes in a mother’s body weight. However, they did discover early menstruation as a possible impact of an increase in weight during pregnancy. Along with early puberty signs in daughters. 

It’s worth noting that the researchers failed to single out the exact mechanism behind the association of obesity with a son’s reproductive health. Still, they suggest that being overweight comes with alterations in the hormonal balance of the mother. This is most likely to have an influence on reproductive health in sons in the long term. In addition to that, the authors indicated overweight accompanies low-grade inflammation that could cause harm to the fetus.

All things considered, it appears that being overweight during pregnancy is one of the fastest ways to disrupt the male reproductive system. This may manifest in adulthood as a reduction in semen quality — showing a great risk for infertility. The researchers concluded that keeping a healthy weight when pregnant is critical to lower the chances of having sons with reproductive health issues in the future.

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