Here's a couple of links you might be interested in having a look at (I'm pretty sure they are ok to post because they aren't commercial at all):

http://cancer.emedtv.com/zofran/zofr...pregnancy.html

http://www.ncbi.nlm.nih.gov/pubmed/15327608

It technically a drug usually used for patients undergoing cancer treatment, but... It's been classed as a category B drug by the FDA which means that although it hasn't been specifically tested on pregnant woman, it's believed to be safe due to the results on pregnant animals. Category A is the safest, then there is B, C, D and X. In comparison, panadol is category A, Sudafed is category C, and nurofen is category C before 30 weeks, and D after 30 weeks.

Only you can be the true judge of how you feel, how sick you are, and whether you think the possible risk of taking the zofran outweighs the risk to the baby based on how sick you are.