It is known from studies that exposure to alcohol during gestation can cause a range of birth defects. But now scientists have drawn up a chronology of when the damage occurs.
The time table for damage was published this Monday in the journal Alcoholism: Clinical and Experimental Research. For this study researchers collected confidential data on drinking patterns - the timing, frequency and quantity - from 992 California women during their pregnancies. Following childbirth, the babies were examined for signs of alcohol exposure, such as below-average height or weight and some head and facial characteristics, including a small head circumference or a flattening of the cleft between the nose and upper lip.
They found that the strongest associations were found during the second half of the first trimester. For every one-drink increase in the average number of drinks consumed daily there were sizable increases (ranging from 12% to 25%) in the risk of physical abnormalities related to fetal alcohol syndrome (FAS).
But researchers found various results among women who had similar drinking patterns, showing that there is no single threshold that triggers fetal alcohol syndrome. While the most significant link to damage was found in weeks seven through 12 of pregnancy, that doesn't mean it's safe to drink earlier or later, the authors said. Some women who drink heavily in early pregnancy have miscarriages, which were not counted in this study. The study also found specific abnormalities linked to drinking in the second trimester. In the third trimester, only birth length was linked to drinking patterns.
“This study was designed to address two challenges in FAS studies,” said Haruna Sawada Feldman, a post-doctoral student in the department of pediatrics under the mentorship of professor Christina Chambers at the University of California, San Diego. “The first challenge concerned obtaining accurate alcohol exposure history from maternal reports that might involve social stigma and recall bias. This study collected information 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. Finally, data were collected with specific details about timing in gestation, dose and pattern.”
The second challenge concerned the quality of information on specific physical features of FAS. “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. “This study used an exposure-blinded expert dysmorphologist to look for these features. Furthermore, potential bias due to subjectivity was reduced because these examinations were conducted in the context of a larger study of more than 70 agents of interest, only one of which was alcohol.”
“Research that links the quantity, frequency and timing of alcohol consumption during pregnancy among humans is virtually non-existent,” added Philip A. May, a research professor in the Gillings School of Global Public Health at The University of North Carolina. “While animal data exist, studies like this one in humans are greatly needed, because extrapolation of concepts from animal models to humans is fraught with complications and problems of translation.”
Both Feldman and May believe these findings reinforce the warning that there is no "safe" level of alcohol consumption during pregnancy. “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 Sawada. “These new findings can also help clinicians quantify the importance of discontinuing alcohol as early as possible.” “Based on our findings, there is no safe threshold for alcohol consumption during pregnancy with respect to selected alcohol-related physical features,” the authors wrote. Pregnant women and women planning on becoming pregnant should abstain from alcohol, they said.
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