Smoking among women from ethnic minorities is increasing
Women from ethnic minorities are more likely to smoke or drink during pregnancy the longer they have lived in the UK, researchers have found.
The British Medical Journal study also showed they were more likely to stop breastfeeding sooner.
The Institute of Child Health team said doctors should not assume ethnic minority women did not smoke or drink.
A maternal health expert said it was "sad" that unhealthy habits became normal among immigrant groups.
The research looked at women taking part in the Millennium Cohort Study who had babies between September 2000 and January 2002.
In 2001-02, 7.6% of the population was from an ethnic minority group - up 44% during the previous decade.
Women from ethnic minority groups are known to be less likely to smoke or consume alcohol than the general population, but the researchers looked at how living in a Westernised society affected their habits.
The researchers studied 6,478 mothers of white British or Irish origin and 2,110 mothers from ethnic minority groups who had either migrated to the UK themselves, or were first or second generation immigrants.
Around a third of British and Irish mothers smoke or drank alcohol during pregnancy, compared with a sixth of all the ethnic minority mothers.
And just 27% of British or Irish mothers breastfed for at least four months, compared with 40% of those from ethnic minorities.
But, among women from ethnic minorities, first and second generation mothers-to-be were more likely to smoke and drink during pregnancy than immigrants.
Professor Catherine Law, of the Institute of Child Health, said: "Health professionals should not underestimate the likelihood of women engaging in risky health behaviours because of their ethnicity."
She said smoking and alcohol consumption rates did vary between ethnic minorities, but that in all the groups studied, the rates were increasing.
Professor Law added: "National policies should promote beneficial health behaviours among all mothers."
In an editorial in the BMJ, Professor Krista Perreira of the University of North Carolina, said increasing migration to developing countries meant changes in smoking and drinking habits would have an impact on women's health in pregnancy.
She said higher incomes, exposure to advertising, integration into Western societies and higher smoking and drinking rates amongst immigrant males could all affect the numbers of ethnic minority women who smoke and drank.
Professor Perreira added: "This research is an important first step in developing programmes and policies that promote the health of immigrant women and their children."
Michael Heard, a spokesman for the Royal College of Obstetricians and Gynaecologists, said: "It is sad, but people become normalised to society's unhealthy habits."
But he said women would all be given the same advice about staying healthy while pregnant, and the problem was ensuring women from immigrant communities and ethnic minorities were able to access health checks.
"Language barriers can exist, and in some cultures you wouldn't access antenatal care in early pregnancy."