A concerning study was publish this month in the November issue of Archives of Pediatric and Adolescent Medicine. The Center for Disease Control sponsored a retrospective study that looked back on the antibiotics women received immediately prior to and during pregnancy and any subsequent birth defects their infants had. They compared these birth defects to birth defects seen in infants born to women who had not taken antibiotics prior to or during pregnancy.
The results were surprising. Women who had taken either of two very commonly used antibiotics for urinary tract infections, Sulfonamides (Bactrim), or Nitrofurantoin (Macrobid) had a significantly increased risk of having a baby with a birth defect.
"Sulfonamides were associated with six birth defects, more than any other class: anencephaly (adjusted OR 3.4, 95% CI 1.3 to 8.8), two left-sided heart defects, hypoplastic left heart syndrome (adjusted OR 3.2, 95% CI 1.3 to 7.6) and coarction of the aorta (adjusted OR 2.7, 95% CI, 1.3 to 5.6), choanal atresia (adjusted OR 8.0, 95% CI 2.7 to 23.4) transverse limb deficiency (adjusted OR 2.5, 95% CI 1.0 to 5.9) and diaphragmatic hernia (adjusted OR 2.4, 95% CI 1.1 to 5.4).
Four defects were associated with nitrofurantoin use: anophthalmia or microphthalmos (adjusted OR 3.7, 95% CI 1.1 to 12.2) hypoplastic left heart syndrome (adjusted OR 4.2, 95% CI 1.9 to 9.1), atrial septal defects (adjusted OR 1.9, 95% CI 1.1 to 3.4), and cleft lip with cleft palate (adjusted OR 2.1, 95% CI 1.2 to 3.9)." (OR = Odds Ratio, CI= Confidence Interval)
Other commonly used medications such as Penicillin, Cephalosporins, and Erythromycin were found to be associated with fewer defects. However, even women taking these medications did have an increase risk of having babies with certain birth defects.
"Women who took Penicillin during pregnancy were three times more likely to have a child with an intercalary limb deficiency than women who had not taken penicillin. Women who had taken Erythromycin during pregnancy were more than two times as likely to have a child with anencephaly or transverse limb deficiency. Lastly, having taken a cephalosporin during pregnancy statistically increased a women's chance of having a baby with an atrial septal defect."
However, before concluding that all the birth defects found associated with these medications were actually caused by them, it is important to remember that it is difficult to ascertain whether it is the infection or the treatment causing the defects. For example, asymptomatic urinary tract infections in non-pregnant women would not warrant treatment. However, failure to treat asymptomatic urinary tract infections in pregnant women can lead to intrauterine growth retardation and low birth weight infants. This is just one of many examples of where it is the infection during pregnancy that does the harm.
It is also necessary to try to tease out what part timing plays in determining if a woman has an infant with a birth defect. Unfortunately, the above study was based on patient recall, which often is not entirely accurate. Women were asked what antibiotics they were given and when during the pregnancy they took them, often long after the actual event. This type of study does not lend itself to gathering very specific information as to what week of pregnancy the women acquired the infection or received treatment. However, the study does provide enough information to make further testing necessary.
These medications need to be evaluated for the risks they may pose and to help doctors decide what medications should be the first line of treatment used if a women does get an infection during pregnancy. Until further studies are done, it would be wise, when possible, to err toward the safer side of the antibiotic spectrum, such as penicillin, erythromycin and cephalosporins and to avoid, the once considered safe, Macrobid.