Is zofran (ondansetron) safe while pregnant?

Yes: Zofran (ondansetron) is class b during pregnancy, and is safe.

Zofran (ondansetron) in pregnancy: Zofran (ondansetron) may be used to treat nausea and vomiting associated with pregnancy. It is listed in category b for pregnancy which means that animal studies have shown no risk to fetus but human studies didn't confirm or are not available. Fetal harm is possible but unlikely.