Women who drink heavily early in a pregnancy - possibly before they know they are expecting - may be increasing the risk of premature delivery, according to a new study.
For the study, researchers recruited 4,719 Australian women and found almost an 80 percent higher risk for those who drank heavily in the first third of pregnancy, then stopped.
The researchers found no evidence of problems for women who drank low levels throughout pregnancy.
In the study, the strongest link between alcohol use and early birth was for women who drank moderately or heavily - several units of alcohol or more a week - during the first trimester, but then stopped completely for the rest of the pregnancy.
The researchers suggested that it was possible that the sudden cessation of alcohol drinking might provoke inflammation, which could harm the developing foetus in some way, although this idea was not tested during the study.
"The risk of pre-term birth is highest for women who drink heavily or at binge levels," the BBC quoted Dr Colleen O'Leary, from the University of Western Australia, who led the study, as saying.
"Women should be advised that during pregnancy, drinking alcohol above low levels increases the risk to the baby and that the safest choice is not to drink alcohol during pregnancy," O'Leary added.
The study is published in the British Journal of Obstetrics and Gynaecology.