BNF states:
"In view of the increased risk of neural tube and other defects associated, in particular, with carbamazepine, lamotrigine, oxcarbazepine, phenytoin, and valproate, women taking antiepileptic drugs who may become pregnant should be informed of the possible consequences. Those who wish to become pregnant should be referred to an appropriate specialist for advice. Women who become pregnant should be counselled and offered antenatal screening (alpha-fetoprotein measurement and a second trimester ultrasound scan)."
I decided to search for the term AFP and I found the following definition:
"Alpha-Fetoprotein (AFP), a member of the albuminoid superfamily, is a fetal/tumor-associated protein that is a marker for certain cancers and congenital defects. Like other members of the albuminoid family, AFP can act as a carrier protein, binding several types of molecules including steroids, bilirubin, fatty acids, retinoids, and flavanoids. Some studies suggest that AFP may also act as a regulator of cell growth and survival."
http://www.rndsystems.com/molecule_detail.aspx?m=1049&gclid=CLrI69Ou7qUCFQkf4QodUhXUog