But pregnant women sometimes also produce antibodies against fetal molecules – for example, if their fetus has a different blood group. Our immune systems make antibodies to recognise foreign molecules, which have the potential to be from dangerous bacteria. Now it seems that increasing levels of antibodies in a mother’s immune system could play a role.Īnthony Bogaert at Brock University, Canada, and his team think that some women who are pregnant with boys develop antibodies that target a protein made by the Y chromosome. The more older brothers a boy has, the more likely he is to be gay when he grows up – an effect called the “ fraternal birth order effect”. Having lots of boys can affect a woman’s immune response
