TUESDAY, Jan. 17, 2012 (HealthDay News) -- It's known that drinking during pregnancy leaves babies vulnerable to a spectrum of abnormalities called fetal alcohol syndrome. Now, a new study pinpoints the latter half of the first trimester as a critical time in the development of some of the syndrome's most telling physical characteristics.
Study authors also stressed that their research illustrates there is no safe amount of drinking during pregnancy, since the amount of drinking that produced these features in infants varied from woman to woman.
"The fact that we didn't find a safe threshold is important," said study author Christina Chambers, an associate professor of pediatrics and family and preventive medicine at the University of California, San Diego. "Not every child of women who drink even very heavily has all the features, so there are certain susceptibility factors that we don't know."
The study appears online Jan. 16 ahead of print publication in the April issue of the journal Alcoholism: Clinical & Experimental Research. The authors say it is one of the first to examine the impact of quantity, frequency and timing of alcohol exposure on the condition.
Thought to affect about 1 percent of the American population, fetal alcohol syndrome can result in physical, behavioral and learning problems. People with the syndrome may have abnormal facial features, such as a smooth ridge between the nose and upper lip, small head size, unusually small-set eyes and shorter-than-average height.
The 992 women in the study were enrolled in the California Teratogen Information Service and Clinical Research Program between 1978 and 2005, which provided confidential risk assessments for any potential toxin exposures during pregnancy. Every three months during the remainder of their pregnancies, they were asked about their use of alcohol and other substances, including specific dates of use, drinks per day, number of binge episodes and maximum number of drinks.
Information about their babies' development was collected after birth, and each newborn was then examined by a dysmorphologist, a specialist in structural birth defects, to look for evidence of fetal alcohol syndrome as well as other conditions.
While higher levels of alcohol exposure were strongly linked to a greater risk of infants born smaller and lighter, with small heads and a smooth ridge between the nose and upper lip, the most significant associations were observed during the second half of the first trimester of pregnancy -- defined as 43 to 84 days after conception.
For every one-drink increase in the daily average number of drinks consumed during this stage of pregnancy, there was a 25 percent higher risk for having a smooth ridge between the nose and upper lip; a 22 percent higher chance of having an abnormally thin upper lip; a 12 percent elevated risk of having a smaller-than-normal head; a 16 percent greater risk of reduced birth weight; and an 18 percent higher chance of reduced birth length.
In addition, the likelihood of shorter birth length was associated with drinking in any trimester, the study found.
"There is almost 40 years of research [on fetal alcohol syndrome], but one of the challenges has been determining what are the windows of risk and the patterns in timing and quantity of alcohol use, and this [study] addresses that," said Tom Donaldson, president of the National Organization on Fetal Alcohol Syndrome in Washington, D.C. "This article very clearly demonstrates that risk begins with any use."
Chambers and her colleagues theorized that alcohol exposure in the first six weeks of pregnancy -- when many women don't yet know they're pregnant -- may result in higher miscarriage rates, although the study did not include women who had miscarriages or stillbirths.
The U.S. Centers for Disease Control and Prevention has more information about fetal alcohol syndrome.