The use of Zofran (or ondansetron) in pregnant women has been widely investigated in recent years, and many researchers have concluded that using Zofran during the first trimester of pregnancy – when nausea and vomiting is at its worst – is linked to a variety of birth defects.  While Zofran has shown effective in calming nausea and vomiting, it has also shown to be quite dangerous to the developing fetus, with the potential to cause birth defects that include growth restriction, cleft lip, cleft palate, congenital heart defects, ventricular septal defects (also known as “hole in the heart”), atrial septal defects, and kidney malformation.
Zofran can readily cross the placental barrier at significant levels, according to a study titled Placental Transfer of Ondansetron during Pregnancy.  According to this study, significant amounts were found in fetal tissue and amniotic fluid.  Another 2011 study titled “Medications Used to Treat Nausea and Vomiting of Pregnancy and the Risk of Selected Birth Defects” suggested that Zofran actually doubles the chance of babies being born with cleft palate.
Despite its known risks, and despite the fact that Glaxo itself admits Zofran has not been tested for use in pregnant women, doctors have not stopped prescribing it to pregnant mothers, and the FDA has not stopped them from doing so.  Doctors have the legal responsibility to inform their patients of all known risks of the medications they prescribe, but they are not prohibited from prescribing medications in ways for which they have not been proven safe.