I took it sparingly during my first trimester. Any day that I wanted to feel halfway normal and not throw up all day. The lawyers found an old tiny study that showed an elevated risk for cleft palate and heart issues which was disproved already by a larger study last year. It's best to take nothing while pregnant, but if the choice is the baby starving to death or taking meds, I choose meds. If you get hospitalized for dehydration and lack of nutrition, the docs will give you Zofran in an IV anyway. I tried motion sickness wristbands, ginger everything first. My babies palate is fine in the ultrasounds. I am now 36 weeks.
There are some lawsuits related to it recently, but my doctor said he's never had a patient with an issue. He's still cautious not to use it though and gave me B6 instead. However, I have several family members who took it for the entire 2nd and 3rd trimester and had no problems. If you're getting dehydrated and can't get enough nutrition, your doctor may have judged that the benefits outweigh the risks for you. You should discuss these concerns with the doctor and find out if he/she still believes it's important.
Ondansetron is the generic for Zofran. Why would you refuse it? It's safe to take or your Dr wouldn't prescribe it to you. There's other meds out there if you don't want to take it. My Dr gave me Diclegis. It helped take the edge off the nausea.