Selected antiepileptic drugs (AEDs) increase the risk of birth defects. To 
assess the impact of influencing AED prescribing practices on spina bifida and 
cleft palate we searched the literature for estimates of the association between 
valproic acid or carbamazepine use during pregnancy and these defects and 
summarized the associations using meta-analyses. We estimated distributions of 
the prevalence of valproic acid and carbamazepine use among women of 
childbearing age based on analyses of four data sets. We estimated the 
attributable fractions and the number of children born with each defect that 
could be prevented annually in the United States if valproic acid and 
carbamazepine were not used during pregnancy. The summary odds ratio estimate 
for the association between valproic acid and spina bifida was 11.9 (95% 
uncertainty interval (UI): 4.0-21.2); for valproic acid and cleft palate 5.8 
(95% UI: 3.3-9.5); for carbamazepine and spina bifida 3.6 (95% UI: 1.3-7.8); and 
for carbamazepine and cleft palate 2.4 (95% UI: 1.1-4.5) in the United States. 
Approximately 40 infants (95% UI: 10-100) with spina bifida and 35 infants (95% 
UI: 10-70) with cleft palate could be born without these defects each year if 
valproic acid were not used during pregnancy; 5 infants (95% UI: 0-15) with 
spina bifida and 5 infants (95% UI: 0-15) with cleft palate could be born 
without these defects each year if carbamazepine were not used during pregnancy. 
This modeling approach could be extended to other medications to estimate the 
impact of translating pharmacoepidemiologic data to evidence-based prenatal care 
practice.