Treating infections is critical to the health of a mother and her baby, according to background information in the article. Therefore, bacteria-fighting medications are among the most commonly used drugs during pregnancy. Although some classes of antibiotics appear to have been used safely during pregnancy, no large-scale studies have examined safety or risks involved with many classes of antibacterial medications.

Krista S. Crider, Ph.D., of the Centers for Disease Control and Prevention, Atlanta, and colleagues analyzed data from 13,155 women whose pregnancies were affected by one of more than 30 birth defects (cases). The information was collected by surveillance programs in 10 states as part of the National Birth Defects Prevention Study. The researchers compared antibacterial use before and during pregnancy between these women and 4,941 randomly selected control women who lived in the same geographical regions but whose babies did not have birth defects.

Antibacterial use among all women increased during pregnancy, peaking during the third month. A total of 3,863 mothers of children with birth defects (29.4 percent) and 1,467 control mothers (29.7 percent) used antibacterials sometime between three months before pregnancy and the end of pregnancy.

"Reassuringly, penicillins, erythromycins and cephalosporins, although used commonly by pregnant women, were not associated with many birth defects," the authors write. Two defects were associated with erythromycins (used by 1.5 percent of the mothers whose children had birth defects and 1.6 percent of controls), one with penicillins (used by 5.5 percent of case mothers and 5.9 percent of controls), one with cephalosporins (used by 1 percent of both cases and controls) and one with quinolones (used by 0.3 percent of both cases and controls).

Two medications -- sulfonamides and nitrofurantoins (each used by 1.1 percent of cases and 0.9 percent of controls) -- were associated with several birth defects, suggesting that additional study is needed before they can be safely prescribed to pregnant women.

"Determining the causes of birth defects is problematic," the authors write. "A single defect can have multiple causes, or multiple seemingly unrelated defects may have a common cause. This study could not determine the safety of drugs during pregnancy, but the lack of widespread increased risk associated with many classes of antibacterials used during pregnancy should be reassuring."

The National Birth Defects Prevention Study is funded by a cooperative agreement from the Centers for Disease Control and Prevention.

Note: If no author is given, the source is cited instead.

• Birth Defects
• Pregnancy and Childbirth
• Down Syndrome
• Gynecology
• Diseases and Conditions
• Infant's Health

• Nutrition and pregnancy
• Fertility
• Maternal bond
• Spina bifida
• Colostrum
• Premature birth