Pregnant women strive to be as healthy as possible by watching what they eat, drink, and do with their bodies to ensure a safe, and healthy baby. Many expectant moms are hesitant to take antibiotics during pregnancy, although they're more vulnerable to getting bacterial infections, specifically UTIs. Now, researchers at the University of Montreal in Quebec have found their fears are validated: antibiotic use is linked to a higher risk of miscarriage, or spontaneous abortions, in early pregnancy.

Read More: Certain Antibiotics May Cause More Harm Than Others During Pregnancy

In the study, published in the Canadian Medical Association Journal, Berard and her colleagues found these five common antibiotics, including macrolides, quinolones, tetracyclines, sulfonamides and metronidazole, posed the greatest risk of miscarriage during the early stages of pregnancy. The average gestational age for miscarriage was 14 weeks of pregnancy; women who miscarried were more likely to be older, living alone, and have multiple health issues and infections. The researchers accounted for this before finalizing their results.

"Although antibiotic use to treat infections has been linked to a decreased risk of prematurity and low birth weight in other studies, our investigation shows that certain types of antibiotics are increasing the risk of spontaneous abortion, with a 60% to two-fold increased risk," said Dr. Anick Berard, author of the study, and Faculty of Pharmacy at the University of Montreal, in a statement.

Data from the Quebec Pregnancy Cohort from 1998 to 2009 revealed over 8,702 cases were clinically detected as spontaneous abortions among women between the ages of 15 and 45 years. The researchers matched these cases with 87,020 controls to determine the influence of antibiotic use and no antibiotic use during pregnancy on miscarriages. A total of 1,428 (16.4 percent) cases were exposed to antibiotics in the early stages of pregnancy compared to 11,018 (12.6 percent) in controls.

"Given that the baseline risk of spontaneous abortion can go as high as 30%, this is significant," said Berard.

Berard and her research team stressed not all antibiotics are linked with a higher risk of miscarriage. For example, a 2009 study in JAMA Pediatrics found penicillins — one of the most common antibiotics used during early pregnancy — are the safest. Penicillins, including ampicillin, amoxicillin, and Augmentin, can be used to treat a UTI, but sometimes it depends on the specific bacteria that is causing the infection. Pregnant women are more susceptible to UTIs because hormones cause changes in the urinary tract, making it more likely for them to get infections.

However, the same study revealed pregnant women taking sulfa drugs and nitrofurantoins (urinary germicides) — both commonly used to treat UTIs — had children with birth defects, such as heart problems, hernias or cleft palate. Sulfa drugs are the oldest antibiotics to date; animal studies have found they do cause harm during pregnancy. Yet, doctors have previously viewed nitrofurantoins as a safe UTI treatment during pregnancy.

In the new study, Berard assured nitrofurantoins, along with erythromycin, were not associated with an increased risk of miscarriage.

Read More: FDA Requires New Safety Labels For Common Antibiotics That Do More Harm Than Good

It's important to note antibiotic use during pregnancy is not strictly forbidden. However, pregnant women should understand when these medications do more harm than good. It's best to consult a doctor and determine the best course of action for your condition.

Source: Muanda FT, Sheehy O, and Berard A. Use of antibiotics during pregnancy and risk of spontaneous abortion. CMAJ. 2017.

See Also:

What Happens If You Stop Antibiotics Early?

New Study Finds That Modifying Antibiotics Could Help Destroy Treatment-Resistant Bacteria