The lead author of the study is Haruna Sawada Feldman, a post-doctoral student in the University of California, San Diego pediatrics department, where senior author Christina Chambers, is a professor. The study is published in the journal Alcoholism: Clinical and Experimental Research.
Fetal Alcohol Syndrome (FAS) is a spectrum of growth, mental and physical abnormalities that can occur in babies whose mothers drink alcohol during pregnancy.
Physical features of serious FAS include smooth philtrum (no groove between nose and upper lip), thin vermillion border (thin upper lip), short palpebral fissures (abnormally small-set eyes), microcephaly (small head circumference), and growth deficiencies in weight and height.
Feldman said in a statement that they designed the study to overcome two key problems in Fetal Alcohol Syndrome research.
One is that FAS research often relies on what the mothers say about their alcohol consumption. Sourcing data in this way raises questions about inaccuracy due to recall bias and social stigma.
Feldman says they overcame this by collecting data during pregnancy when women were unaware of their pregnancy outcome.
"The data were also collected by trained counseling specialists who had built a rapport with the woman and guaranteed confidentiality while collecting sensitive information," said Feldman.
An added bonus of getting the data in this way was that it included specific details about the stage of pregnancy, dose and pattern of alcohol consumption.
The other difficulty with FAS research is spotting the symptoms in newborns. This requires a careful examination of specific physical features:
"These alcohol-related features are often subtle, and a non-expert examiner may miss or misclassify features, and/or can be biased by subjectivity, especially if he/she suspects or knows about prenatal alcohol exposure (PAE)," said Feldman.
To overcome this second challenge, the study used an expert in dysmorphology, someone trained to look for physical abnormalities, including very subtle ones.
And the expert was exposure blinded, that is they did not know which of the babies they were examining were suspected of having FAS, and further potential bias was reduced because the exams were done in the context of a larger piece of research that was looking at over 70 different variables, of which effects of alcohol was only one.
The data for the study came from 992 women and their single babies in California gathered between 1978 and 2005. It included patterns of drinking and timing of alcohol exposure in relation to selected FAS features.
Patterns of drinking were assessed in terms of drinks per day, number of binge episodes and maximum number of drinks.
Timing of exposure was evaluated for zero to six weeks after conception, six to 12 weeks after conception, and during the first, second, and third trimesters.
The results showed that:
- Higher prenatal alcohol exposure in every alcohol consumption pattern was significantly linked to an increased risk of the baby being born with reduced birth weight or length, having a smooth philtrum, thin vermillion border or microcephaly.
- The most significant links were during the second half of the first trimester.
- During this period of gestation, for every increase of one alcoholic drink in the average daily consumption, there was a 25% increase in risk for smooth philtrum, 22% increase in risk for thin vermillion border, 12% for microcephaly, 16% for reduced birth weight, and 18% for reduced birth length.
"Women should continue to be advised to abstain from alcohol consumption from conception throughout pregnancy," they add.
Feldman said the fact they found no links during the first half of the first trimester between alcohol consumption and FAS signs should not be taken to mean it is safe to drink alcohol during this stage of pregnancy.
Their study only took into account live births and so did not include women who may have miscarried or had stillbirths.
"It is important to know that alcohol-exposed infants who would have exhibited alcohol-related minor malformations might also be more likely to be lost to miscarriage following exposure during the first six-week window," warned Feldman.
"Clinicians should continue to follow the recommendations to encourage women who are planning a pregnancy or have the potential to become pregnant to avoid alcohol, and to advise women who become pregnant to stop alcohol consumption," said Feldman.
"These new findings can also help clinicians quantify the importance of discontinuing alcohol as early as possible."