About one in six sudden infant deaths may be linked to heavy alcohol use by their mothers during or soon after pregnancy, according to an Australian study.

One of the morals of the story is that parents should be very careful about drinking alcohol, especially if you’re a single parent because there is no other parent to back you up

Researchers writing in Paediatrics found that those deaths may result from babies being exposed to alcohol in the womb and from alcohol-using mothers creating hazardous environments for the babies after birth.

“The results of this study indicate that maternal alcohol-use disorder increases the risk of infant death syndrome (SIDS) and (infant deaths) through direct effects on the foetus and indirectly through environmental risk factors,” wrote researchers led by Colleen O’Leary from Curtin University in Perth, Australia.

The US Centres for Disease Control and Prevention (CDC) defines sudden SIDS as the death of a child under one year with no obvious cause. Approximately 4,500 infant deaths fall into this category every year in the US, according to the CDC.

Previously, researchers have tied SIDS to parents’ smoking and to unsafe environments, but few studies have looked at whether alcohol could be involved in some of the deaths.

The study team examined information on 77,895 women who gave birth between 1983 and 2005, comparing the number of SIDS and infant deaths that occurred in children of mothers with a diagnosed drinking problem, to cases among the children of mothers without a diagnosis.

Overall, 171 SIDS cases occurred during that time in children born to the 21,841 women who were diagnosed heavy drinkers. Among the children who were born to 56,054 mothers without a diagnosis, there were 132 SIDS cases.

The researchers found that children born to mothers who drank heavily during pregnancy had a sevenfold increase in the risk of SIDS, compared to children of mothers without a drinking problem.

Babies also had a ninefold increased risk of SIDS when their mothers drank within the year after birth, compared to babies born to mothers who did not drink.

“One of the morals of the story is that parents should be very careful about drinking alcohol, especially if you’re a single parent because there is no other parent to back you up,” said David Phillips, a professor at the University of California, San Diego, who has studied alcohol-related infant deaths but wasn’t involved in the story.

He pointed out that the study found a link between infant deaths and a mother’s drinking as long as one year after giving birth. “So it can’t just be a biological explanation of what’s going on,” he said.