Why couples with daughters are more likely to divorce

The reason parents of girls are more likely to divorce may surprise you.
The reason parents of girls are more likely to divorce may surprise you. Photo: Getty Images

It may have been the case back in Medieval times when Kings needed to produce a boy to be next in line to the throne. However new research has shown the higher rate of marriage breakdowns between parents who have daughters has nothing to do with a father's preference for sons.

Couples with daughters have been shown to have slightly higher divorce rates than those who have boys. Up until now it has been assumed that was due to dads having a preference for sons and therefore being happier in their marriage if it produces at least one boy.

However findings of a new study have thrown the dads preferring sons theory out the window. 

Researchers from Duke University in the US found female embryos are actually more hardy and robust while in the womb, and therefore more likely to survive if their mother experiences high stress levels during pregnancy, than male embryos. This results in more daughters than sons being born into already tense marriages.

"Many have suggested that girls have a negative effect on the stability of their parents' union," said co-author of the new study Duke economist Amar Hamoudi. "We are saying 'not so fast'."

Hamoudi and his team came to their conclusion after studying longitudinal data from a sample of US residents from 1979 to 2010. Not surprisingly, they found a couple's level of relationship conflict predicted their likelihood of eventually heading to divorce court.  

More interestingly, researchers found that a couple's level of relationship conflict also predicted the sex of children they would have in the future. Essentially, women who reported higher levels of marital conflict were more likely to give birth to girls rather than boys.

According to the research paper, published in US journal Demography, stressful situations can lead to unhealthy levels of important hormones, which can then lead to reduced fertility. This is because the biological system that regulates stress hormones has an influence on the system that regulates progesterone - a hormone necessary for an early pregnancy to be successful.

"Girls may well be surviving stressful pregnancies that boys can't survive," Hamoudi said. "Thus girls are more likely than boys to be born into marriages that were already strained."

The Duke researchers point out their theory about females being the gender more capable of coping with difficult conditions is backed up by survival rates throughout male and female lifetimes. At every age from birth to age 100, boys and men die at greater rates than girls and women, they explained.