A neuroscientist contends that women who smoke or use drugs during pregnancy could increase the likelihood of her child being gay, The Daily Mirror reported.

In his new book, "We Are Our Brains," Dr. Dick Swabb claims the sexuality of an unborn child is influenced by "the lifestyle led by its mother," The Daily Mirror reported. He said this is because brain development during pregnancy and early childhood is directly linked to the kind of people "we become in adulthood," DNA India reported.

He writes in the controversial book that brain development during pregnancy is altered by the tiniest chemical changes.

"Pre-birth exposure to both nicotine and amphetamines increases the chance of lesbian daughters," Swaab is quoted as saying by The Sydney Morning Herald.

Swaab, a professor of neurobiology at Amsterdam University, also suggest that factors ranging from taking synthetic hormones to leading a stressful life can increase the likelihood of having a child who turns out to be gay.

"Pregnant women suffering from stress are also more likely to give birth to homosexual children, because their raised levels of the stress hormone cortisol affect the production of fetal sex hormones," Swaab is quoted as saying in his new book by The Daily Mirror.

He also claims that a child with more older brothers increase the likelihood of it turning out to be gay.

"The more older brothers a boy has, the greater the chance that he will be homosexual," Swaab is quoted as saying in his new book by The Daily Mirror. "This is due to a mother's immune response to male substances produced by boy babies in the womb, a response that becomes stronger with each pregnancy."

In his new book he multiple academic studies showing how a pregnant mother's lifestyle can possibly affect her child, News.com.au reported. This includes a study showing that women whose moms were given synthetic estrogen while they were pregnant between 1939 and 1960 in order to cut the miscarriage risk had a greater chance of having daughters who were bisexual or lesbian.

He added that smoking, drinking and taking drugs designed to combat depression during pregnancy can also lower a child's IQ, while living in an area with high levels of traffic pollution can raise the risk of autism.