Women who smoke tobacco during pregnancy increase the risk of having children who develop psychotic problems, according to researchers in the U.K., and the expectant mothers who smoked the most faced the greatest risk.

HealthDay News reported Oct. 1 that researcher also reported a link between psychosis and consumption of more than 21 units of alcohol weekly during pregnancy.

Researchers said that maternal smoking may hinder development of the fetal brain. "If our results are non-biased and reflect a causal relationship, we can estimate that about 20 percent of adolescents in this cohort would not have developed psychotic symptoms if their mothers had not smoked," said study author Stanley Zammit at the Cardiff University School of Medicine in Wales. "Therefore, maternal smoking may be an important risk factor in the development of psychotic experiences in the population."

The study was published in the October 2009 issue of the British Journal of Psychiatry.