Women stressed out before pregnancy nearly twice as likely to have a girl

GRANADA, Spain — Can your stress level during conception play a role in the sex of your child? According to researchers at the University of Granada, women who are stressed before pregnancy are almost twice as likely to have a girl.

Researchers are not sure why, but one theory is that high concentrations of stress hormone cortisol have a knock-on effect on sex other hormones which influence the child’s sex. Another possibility, is that sperm carrying the X chromosome — which determines the child will be a girl, are less affected by problems with cervical mucus caused by stress.

However, study authors believe one of the most likely explanations is that more male babies are miscarried due to stress. It’s a phenomenon which scientists do not yet fully understand, but think could be an evolutionary adaptation.

For the study, researchers analyzed hair samples from 108 pregnant women to detect levels of cortisol. Tests were carried out between weeks eight and 10 of pregnancy, with the hair follicles showing levels of stress going back months. The women also underwent a series of psychological tests to find out how stressed they were.

“The results we found were surprising, as they showed that the women who had given birth to girls presented higher concentrations of hair cortisol in the weeks before, during, and after the point of conception than those who had boys,” says Dr. María Isabel Peralta-Ramírez, from UGR’s Department of Personality, Evaluation and Psychological Treatment, in a university release.

The cortisol concentrations in the hair of mothers who had girls were almost double that of those who had boys.

Previous studies have shown the negative impact of stress on the mother in the processes of pregnancy, birth, and even infant brain development.

“Specifically, our research group has shown in numerous publications how psychological stress in the mother generates a greater number of psychopathological symptoms during pregnancy, postpartum depression, a greater likelihood of assisted delivery, an increase in the time taken for lactation to commence, or inferior neurodevelopment of the baby six months after birth,” says Dr. Peralta-Ramírez.

“All of the existing research tells us about the effect of stress when pregnancy has already occurred,” she adds. “However, few studies have shown the link between stress and the mother-to-be before or during the conception of the baby, the present study being a rare exception.”

One possible explanation for the results could be that the activation of the “stress system” — the hypothalamus-pituitary-adrenal gland system — which involves an increase in cortisol production, changes the amounts of sex hormones at the time of conception.

But the mechanisms behind this change are not well understood because of contradictory effects.

On the one hand, higher levels of stress boost testosterone, which is known to produce male babies. On the other, there is scientific evidence that sperm carrying the X chromosome, which determines that the baby will be female, perform better at passing through the cervical mucus in “circumstances of adversity” caused by stress.

“There are other possible hypotheses that attempt to explain this phenomenon,” says Dr. Peralta-Ramírez. “Among the strongest theories is the idea that there are more terminations of male fetuses on medical grounds during the first weeks of gestation in situations of severe maternal stress. That said, in light of the design of these studies, it is recommended that the results are corroborated in greater depth.”

However, several studies have shown fetuses are vulnerable to the effect of stress, since it plays a key role in their development.

An example of this is the proven fact that male fetuses mature more slowly than females. They tend to be associated with more complications in pregnancy and premature delivery and, at birth, they are more likely to have shorter telomeres, the “caps” on the end of chromosomes.

This means male fetuses are more vulnerable to adverse prenatal environments, suggesting that women who experience high levels of stress around the time of conception may be less likely to give birth to a boy.

The findings are published in the Journal of Developmental Origins of Health and Disease.

SWNS writer William Janes contributed to this report.

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