Are stressed moms more likely to have daughters?

Posted on January 18, 2012


Image: Sam Pullara/Wikipedia

Dateline: 17 October 2011 // Posted by: Gareth Keane

Source: Daily Mail

Story: “Why stressed-out women are more likely to have girls”

Summary: Scientists in Oxford University in conjunction with scientists working in the US claim to have found that women who are stressed in the weeks and months leading up to pregnancy have significantly higher odds of having a girl rather than a boy. The scientists say that this stress can occur in a number from a number of different sources such as being under pressure at work, at home or in their love lives.

The study examined 388 women who were trying to get pregnant and living in the United Kingdom. These women were asked to keep a diary relating to their sex lives and their lives in general. The scientists measured the self-purported stress levels of the women by getting the women to fill out a questionnaire relating to how stressed they felt, and also measured their levels of cortisol in the months leading up to pregnancy.

The research claims that somehow in cases where women have higher levels of cortisol in their bloodstream it is harder for the male embryos to implant in the womb. In addition the report claims that boys who are born may be fragile and so there is a higher risk of a miscarriage occurring with the consequence of more girls being born.

Why is this PseudoNews? There are several erroneous statements throughout the study which throw suspicion on the validity of the findings, which is the first ever study to link the stresses of everyday life to higher chances of having a girl.

Firstly as it is the male sperm that determines the sex of the child it is an extraordinary claim to suggest that as a result of the stresses in a woman’s everyday life the sperm are differentiated between and the female ones are more likely to fertilise the egg, and sufficient evidence is not shown to back this up. The study also does not take into account the stress levels of the men from whom the sperm comes.

Interestingly the actual quantitative results of the experiment are not given with the report just saying “among the 50 per cent of the women who had the highest amounts of cortisol before pregnancy, the sex ratio was clearly skewed towards girls”. Despite stating the earlier claims as fact the study does admit near the end that it “only studied a small number of women and more work is needed to confirm the finding”. This flaw is a warning sign that adequate levels of scientific protocol were most likely not adhered to in this particular study.

Furthermore Dr. Allen Pacey, a fertility expert from Sheffield University, claimed that while the results were interesting they did not show that stress was the actual cause of the lack of boys being born. The news report then suggests other possible causes being nutrition and simple biological reasons.

What features of pseudoscience are on show? First and foremost this study clearly lacks parsimony. With so many possible confounding variables which may affect the findings it jumps to the conclusion that is the stress levels of the woman that causes a girl to be born.

This is also linked to the problem of a lack of experimental control which I have alluded to earlier. The experiment is not properly designed in a framework that would allow the high stress levels of the women to be the only factor which would influence the chances of a girl being born.

The study is also susceptible to confirmation bias as the findings of the women with high stress levels who did have boys were just ignored.

The moral of the story: This study simply fails to live up to the extraordinary hypothesis it put forward. It falls victim to several pseudoscientific features yet continues to purport itself as science. The study should be read with a high degree of scepticism and the further study in this area which is due to commence should also be thoroughly examined in order to assess its validity.