A neuroscientist has said that pregnant women who smoke increase the chances of affecting their child’s sexuality and intelligence.

Dick Swaab, a professor of neurobiology at Amsterdam University told the Sunday Times that as well as smoking, drinking, taking drugs and living in an area with a lot of pollution can affect children as they grow older.

He said that smoking can increase the chances of a girl being lesbian or bisexual, and that stress was also a factor, with more stressed mothers increasing the chance of their child of either gender being gay.

Having more older brothers increased the risk of boys being gay, he said, because the development of a mother’s immune system has stronger responses to male hormones with each boy born.

Swaab also said that drinking and taking drugs can lower a child’s IQ.

“Pre-birth exposure to both nicotine and amphetamines increases the chance of lesbian daughters,” Swaab told the Sunday Times.

“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.”

Saying that foetus brains begin to develop at two weeks, Swaab said anything which allows toxins into the body could have an impact on development, and noted studies between 1939 and 1960 which showed that women who took synthetic oestrogen decreased the risk of miscarriage, but increased the chance of bisexuality or lesbianism in their daughters.

Swaab continued: “In women who drink a lot, cells that were meant to migrate across the foetal brain can end up leaving the brain altogether.”

Swaab did concede that lifestyle was only one factor, with genetics playing the strongest role. He said the research proved that the development of the brain during pregnancy is directly impacted by adult lifestyles.