A study carried out at the University of Granada monitored 108 women from the first weeks of pregnancy through to delivery.

The pregnant women’s stress levels were measured via the concentration of cortisol in their hair at 8-10 weeks of pregnancy. The level of cortisol represented the previous three months (one month per centimetre of hair growth), that is the period before and after conception. Variables relating to the birth and sex of the baby were recorded later.

The study found that women who gave birth to girls had double the concentration of hair cortisol in the weeks before, during, and after conception than women who had boys.

Research to date demonstrates the impact of stress when conception has already occurred. However, few studies have shown the link between stress and the mother-to-be before or during the conception of the baby. One explanation for the study’s findings is that the activation of the hypothalamus-pituitary-adrenal gland ‘stress system' modifies the concentration of sex hormones at the time of conception. There is also evidence that sperm carrying the X chromosome are better able to pass through the cervical mucus in circumstances of adversity and therefore more likely to be successful in reaching the egg.

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Read more: Peralta-Ramirez, M.I. (2021) Hair cortisol levels in pregnancy as a possible determinant of fetal sex: A longitudinal study. Developmental Origins of Health and Disease. DOI: https://doi.org/10.1017/S2040174420001300

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Relevant article in the IJBPE:

Buklijas, T. (2021) Developmental Origins of Health and Disease: What it means and why it matters. IJBPE, Volume 8, Issue 3:3-7.

Sher, J. (2017) Making preconception health, education and care real. IJBPE, Volume 4, Issue 4:4-8.

Music, G. (2013) Stress pre-birth: How the fetus is affected by a mother’s state of mind. IJBPE, Volume 1, Issue 1:12-15.