(UTIs) can be problematic for pregnant women and their babies, but so can two antibiotics used to treat these infections, U.S. health officials warn.
The antibiotics -- trimethoprim-sulfamethoxazole (Bactrim) and nitrofurantoin (Macrobid) -- have been linked to a small risk forin pregnant women when given in the first trimester.
Despite the risk, many pregnant women are still getting these, according to a new report from the U.S. Centers for Disease Control and Prevention.
"Birth defects associated with these drugs include heart, brain and facial defects," said Elizabeth Ailes, a health scientist at the CDC and lead author of the report.
A 3 percent risk of birth defects is associated with all pregnancies, she said. "The increased risks associated with these antibiotics is relatively small, but significant -- about two-times," she said.
About 8 percent ofdevelop UTIs.
"It's important for women to know, despite the small elevation in birth defects risk, treatment is really important because untreated UTIs can have serious consequences for both the mom and the baby," Ailes said.
Untreated, these infections can lead to babies born at a low birth weight, babies born prematurely and the development of body-wide infections that can be deadly, she said.
Among privately insured women with UTIs, about 40 percent are being prescribed Bactrim or Macrobid, according to Ailes.
If a UTI can be cured only with either of these drugs, however, they need to be used regardless of the small risk, said Dr. Jill Rabin, chief of ambulatory care, obstetrics and gynecology and head of urogynecology at Northwell Health in New Hyde Park, N.Y.
Rabin also said that these antibiotics, like any other drug, should be prescribed at the lowest effective dose.
The American College of Obstetricians and Gynecologists recommended in 2011 that such drugs be prescribed in the first trimester of pregnancy only when other drugs would not be an appropriate treatment, according to the CDC report.
However, one problem with the report, Rabin said, is that "we don't know if these medications were prescribed appropriately based on adjusting the dose and type of antibiotic and on the particular bacteria causing the infection."
The 2011 recommendation about not using these antibiotics to treat UTIs in the first trimester might not have filtered down to all physicians, another doctor noted.
"A number of previous studies have shown that expert guidelines do not always find their way into bedside practice," said Dr. Michael Grosso, chief medical officer at Huntington Hospital in Huntington, N.Y.
One reason for this is the increasing volume of medical literature, which means more new information is available than any physician can read, Grosso said. In addition, he said that doctors may disagree with a guideline.
"Although a physician may avoid these medications when he knows a patient is pregnant, he may not go so far as to order pregnancy testing prior to every prescription, thus leaving open the door to inadvertent use in the setting of pregnancy," Grosso said.
Concerned patients should ask their doctor if prescribed medications are safe if they might be pregnant, he advised.
For their research, Ailes and her colleagues analyzed data on nearly 483,000 women who were pregnant in 2014 and covered by employer-sponsored insurance. The data came from the MarketScan Commercial Database.
Rabin questioned whether the data was representative of prescriptions given all pregnant women or whether the finding that these drugs were commonly prescribed applied only to those represented in the database.
"I think it's premature to draw a sweeping conclusion with this study," Rabin said.
The report was published Jan. 12 in the CDC's Morbidity and Mortality Weekly Report.
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