The study, which is slated to be published in the journal Alcoholism: Clinical & Experimental Research in April, found that the amount of alcohol required to create health problems is different for each woman and child.
This means that there is no way to safely drink alcohol during pregnancy, since a mother can't know what her baby's threshold is.
The study used data obtained by counselors at the California Teratogen Information Service Pregnancy Health Information Line, focusing on 922 women in California over 27 years.
Research showed that drinking alcohol during pregnancy boosted the risk of having an underweight newborn or a baby with a shorter length at birth.
Deformities associated with fetal alcohol syndrome include small head, small upper jaw, smooth and thin upper lip and small, narrow eyes.
When women drank alcohol between the seventh and 12th weeks of their pregnancies, the risks of problems with their baby's lips increased by 25 percent per drink, the chance of a shorter length at birth increased by 18 percent, the chance of reduced birth weight increased by 16 percent and the risk of smaller head size at birth went up by 12 percent.
Christina Chambers, a professor of pediatrics at UC San Diego, pointed out that the results of the study should not be misinterpreted to mean that drinking during the first seven weeks of pregnancy is safe.
Chambers also emphasized that the study only looked at data surrounding live births and did not include data from women who had miscarriages or stillbirths possibly resulting from early alcohol exposure.
