Research published in The Proceedings of the National Academy of Sciences analysed the ways in which maternal pre-natal stress can influence birth outcomes. It found that those who were reported to feel stressed, were more likely to have girls than boys.
The study examined indicators of physical, psychological and lifestyle stress collected from diaries, questionnaires and daily physical assessments of 187 healthy pregnant women.
Their finding showed a third of the women were stressed – with 17 percent being psychologically stressed (with high levels of depression and anxiety) and 16 percent being physically stressed (with large calorie intakes and higher blood pressure).
Despite there being 105 males born for every female birth on average, the sex ratio of births in the physically and mentally stressed group in the study indicated larger amounts of female births. The psychologically stressed had a 2:3 male-to-female ratio and the physically stressed had a 4:9 male-to-female ratio.
So, why are we seeing more female births in individuals of those who are reported to feel stressed? The researchers have suggested that it could be down to the fact that male foetuses are more susceptible to adverse conditions in the womb.
The outcomes of this research mirror other studies that reveal the way trauma and stress can up the chances of giving birth to women.