Researchers have uncovered the truth behind two of the most commonly antibiotics and whether they cause birth defects in women.

In reality, azithromycin and clarithromycin are perfectly safe for women during pregnancy, despite growing concerns that they may be connected to birth defects in children, according to a UPI report.

The drugs are part of an antibiotics group called macrolides. Macrolides have a molecular structure that has a macrocyclic lactone ring with at least one sugar attached, and they are typically used instead of penicillin in patients who are allergic. It’s the latest salvo in a debate over just how significant a health threat antibiotics can be to unborn fetuses.

The big concern about macrolides has been that pregnant women who are allergic to penicillin may be risking birth defects in their unborn child by taking them, but Dr Anick Berard of the University of Montreal said in a statement that there was no evidence this is the case.

The researchers made this determination by looking at data between 1998 and 2008 from the Quebec Pregnancy Cohort. It was a very large study involving 135,869 pregnancies, with 1.7 percent of them involving a pregnant woman who was taking macrolides in the first trimester. Compared to 9,106 women who took penicillin, about 914 took azithromycin, 734 took erythromycin, and 686 took clarithromycin.

The study found that 9.8 percent of women gave birth to a child with a major congenital malformation, but there didn’t appear to be an noticeable difference in women who took different antibiotics.

The findings were published in the journal Pharmacoepidemiology and Drug Safety.