This "groundbreaking" claim was made by neurobiologist Dick Swaab from Amsterdam University. The study claims that a women's lifestyle choices during pregnancy can not only affect the development of their children, but that smoking during pregnancy may actually increase the likelihood that a child will be gay:
Pre-birth exposure to both nicotine and amphetamines increases the chance of lesbian daughters.

Pregnant women suffering from stress are also more likely to have homosexual children of both genders because their raised level of the stress hormone cortisol affects the production of foetal sex hormones.
This apparently is also linked with how the mother's immune system has a stronger response to all those male hormones.

Obviously, we don't encourage women to smoke and get wasted while pregnant. But this study is about as plausible as claiming that women who eat chocolate mousse are far more likely to have the devil's baby.

[Telegraph]