The conclusions of the study were based on data from 1,349 infants in Sweden whose mothers took Zofran in early pregnancy between 1998 and 2012.
Zofran was associated with a statistically significant increased risk of heart defects, including a doubled increased risk of “hole in the heart” defects (also known as cardiac septum defects).
The researchers did not find any increased risk of birth defects in general, but after noting a “likely” increased risk of septal defects, they warned:
“[I]f an association between the use of ondansetron and an increased risk for cardiovascular defects is true, the strongly increasing off label use of the drug at nausea and vomiting in early pregnancy must be regarded as unsuitable and should be avoided.”
Septal heart defects include atrial septal defect and ventricular septal defect. They are the most common heart defects.
These defects occur in the first few weeks of pregnancy, when the heart is dividing into four chambers. The septum is a wall between the two upper chambers (“atria”) and lower chambers (“ventricles”). If it does not form completely, holes remain and the baby is born with a heart defect.