Page last updated: , November 11, 2010
Prenatal alcohol exposure and risk of birth defects

A study from Western Australian examined the associations between dose, pattern, and timing of prenatal alcohol exposure (PAE) and birth defects.
Data from a randomly selected, population-based cohort of nonindigenous women who gave birth to a live infant in Western Australia (WA) between 1995 and 1997 (N = 4714) were linked to WA Midwives Notification System and WA Birth Defects Registry data. Researchers assessed the associations of PAE before pregnancy, in the first trimester, and in late pregnancy with any birth defect and with birth defects classified as alcohol-related birth defects (ARBDs) by the Institute of Medicine (IOM), by using logistic regression.
Information about maternal alcohol consumption was collected 3 months after birth for the 3 month period before pregnancy and for each trimester. Low alcohol consumption was defined as less then 7 standard drinks (10g) a week, and no more than 2 drinks on any one day. Moderate use was defined as up to 70g of alcohol a week, with the majority of women consuming 21-49g per occasion.  Women who engaged in binge drinking of more that 50g per occasion less than once a week were also included in the moderate drinkers group. Women who consumed more than 70g per week were classified as heavy drinkers and women consuming more than 140g were classified as very heavy drinkers.
The study results indicate that the prevalence of birth defects classified as ARBDs by the IOM was low. Compared with abstinence, heavy prenatal alcohol exposure in the first trimester was associated with increased odds of birth defects (adjusted odds ratio: 4.6 [95% confidence interval: 1.5-14.3]), with similar findings after validation through bootstrap analysis. There was no association between low or moderate prenatal alcohol exposure and birth defects.
The study authors conclude that  although a large proportion of women in the cohort consumed alcohol during pregnancy, the prevalence of any birth defects classified as ARBDs by the IOM was low (2.3%). A significant fourfold increase in birth defects followed heavy prenatal alcohol exposure during the first trimester. Many individual birth defects included in the IOM classification for ARBDs either were not present in this cohort or were not associated with prenatal alcohol exposure. The authors suggest that large, population-based studies are needed to strengthen the evidence base for ARBDs and that screening and documentation of alcohol use by women of childbearing age and pregnant women would enhance surveillance efforts and inform prevention.

Source: Prenatal Alcohol Exposure and Risk of Birth Defects; E Geelhoed, E.J. Elliott and C Bower C. M. O’Leary, N. Nassar, J.J. Kurinczuk, N. de Klerk, Pediatrics 2010;126;e843-e850; originally published online Sep 27,

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