Huybrechts KF, Hernandez-Diaz S, Straub L, et al. - Experts carried out a follow-up study to investigate the relationship between IV ondansetron and congenital malformations. A population-based cohort study formerly assessed the relationship between first-trimester exposure to the oral formulations of ondansetron and congenital malformations. Following accounting for possible confounding variables, no important correlation with congenital malformations overall or cardiac malformations were noted, however, a minute increase in the risk of oral clefts could not be eliminated. Succeeding research implied that the IV administration of ondansetron may be related to higher risks of cardiac malformations and oral clefts. Potential specifications for the apparent discrepancy in teratogenic effect of IV in comparison with oral formulations involve residual confounding by indication and related factors (eg, nutritional deficiencies) in women with hyperemesis critical enough to need IV medication, higher doses administered intravenously compared with orally, and greater specificity for exposure since studies of oral use in healthcare utilization data are on the basis of distributed medication, and not all women may take the medication as prescribed.