Ask a pharmacist. Or google the medication - some of them you'll find the information online somewhere.

A pharmacist and my ob told me that rhinocorte was fine to take when pregnant, as it's a category A drug in the nasal-spray form. It worked to alleviate my hayfever just fine.

Personally I wonder how many people who wouldn't let even a category A drug into their body while pregnant will happily drink different herbal teas and suchlike, without even wondering whether the effects of those concentrated things have been well studied in pregnant women. Just because something is "natural" doesn't mean it is not harmful.