A new study suggests a link between some antibiotics doctors prescribe for women with urinary tract infections and certain birth defects.

The research, published in the November issue of the Archives of Pediatrics and Adolescent Medicine found a correlation between certain antibiotics in two categories of antibacterials, sulfonamides and nitrofurantoins, and certain severe birth defects. Bactrim falls into the former category, Macrobid the latter.

Researchers looked at data for 13,155 women who took antibiotics from one month before their pregnancies started through the end of their first trimesters.

The researchers saw an association with sulfonamides and nitrofurantoins and serious defects like blockages of the nasal passageways and brain and skull abnormalities.

Importantly, not all antibiotics were implicated. As the researchers wrote in the abstract or summary of their research article:

Reassuringly, penicillins, erythromycins, and cephalosporins, although used commonly by pregnant women, were not associated with many birth defects. Sulfonamides and nitrofurantoins were associated with several birth defects, indicating a need for additional scrutiny.

In other words, the researchers are calling for more studies. Results like these would seem to demand them.