How safe is keflex in first trimester?

Probably safe: Keflex is considered safe (category b) for 2nd and 3rd trimesters, but it has not been as thoroughly tested during the 1st trimester. Use only if no other options., and discuss your concerns with your doctor.

Safe: Generally considered safe. It is a category b. A is safest but to get an a there has to be scientific studies showing safety. Because these studies are very difficult to perform ( who wants to take a med to see if it is safe in pregnancy) very few drugs are category a. Cat b is about as good as it gets.