External harmful factors, such as stress, pollution or smoking around conception have been associated with a reduction in the number of males, and suggest male embryos are more vulnerable for some reason.
Aspirin is a non-steroidal anti-inflammatory used to treat pain, fever and inflammation. Several small trials have shown that it increases the pregnancy rate among women undergoing IVF.
In the latest study, researchers at the Eunice Kennedy Shriver National Institute of Child Health and Human Development in the U.S. gave 1,228 women who had a history of miscarriages a low-dose aspirin to take before sex or a placebo pill (folic acid) for as long as they were attempting to get pregnant.
Thirty-one per cent on aspirin had a boy, compared to 23 per cent on the placebo. And those on aspirin who had boys had reduced inflammation, suggesting the drug had an effect.
Aspirin before conception seems to ensure the chance of a male embryo being rejected is reduced, says Professor Simon Fishel, president of CARE Fertility clinics.
‘It is a very interesting conclusion and more studies are needed to confirm if it is a potential solution to the apparent excess of female babies for women with evidence of inflammation.
‘Importantly, it relates only to women who have had miscarriages and evidence of inflammation. It does not have any bearing on sex ratios in normal conceptions where aspirin will not increase the chances of having a boy.’