Are they safe?
A: Most antibiotics are Class A and B (sometimes C) medications (see classification HERE) and are thus mostly safe in pregnancy. To find out more, you should look up the category of the antibiotic you are supposed to take.
In many cases you need an antibiotic to treat an infection, and benefits far outweight possible risks. If you do not take the antibiotic when you need it then the risks of an untreated infection is far higher compared to any theorical risks from taking the medication.
For specific antibiotics see HERE.