I realize your concern about antibiotics in pregnancy. Both of the antibiotics that you mentioned are from the same family, both are Macrolides. Both have effect on almost the same type of infections and work similarly.
However Azitromycin is considered a type B drug in pregnancy states, this means that there is no known association with birth defects or other pregnancy-related complication and the drug is probably safe.
Clarithromycin falls into category C meaning that either there isn't enough information or there are some concerns arising from animal studies, but no confirmation of problems like birth defects in humans.
I will suggest you to comply with Azithromycin since it’s safer, if you have any doubt on how to take it, don’t hesitate to ask your physician. I wish you a successful pregnancy.
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