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Prescribing decisions for women of childbearing potential change completely once a drug's teratogenicCapable of causing a birth defect if taken during pregnancy.Read more → risk is established — teratogenic meaning capable of causing birth defects. Valproate is the clearest psychiatric example: its risk profile is why UK regulators treat it as an absolute contraindication in pregnancy outside a strict safety programme. Two separate harms drive this policy — physical malformations and long-term neurodevelopmental problems in the child.

Valproate crosses the placenta freely and reaches the fetus at concentrations similar to maternal blood. It disrupts folate metabolism and inhibits histone deacetylase enzymes, both needed for normal neural tube closure in the first four weeks of pregnancy — often before a woman knows she is pregnant. For example, this early, folate-related mechanism explains why neural tube defects (failure of the spine or brain to close properly) are the most classic valproate-associated malformation.

A vignette raises this concept when a woman of childbearing potential is being started on, or is already taking, valproate for epilepsy or bipolar disorder, and the question asks about pregnancy counselling, contraception requirements, or which malformation to expect on antenatal scan.

Unlike lamotrigine and levetiracetam, which carry substantially lower malformation risk in pregnancy and are preferred where clinically appropriate, valproate carries the highest teratogenicCapable of causing a birth defect if taken during pregnancy.Read more → risk among commonly used anti-seizure medications. Confusing valproate's risk with that of newer anticonvulsants is a common exam trap — the safety advice differs sharply by drug, not just by drug class.

A common trap is assuming the risk is limited to neural tube defects; valproate also raises the risk of cardiac defects, cleft palate, hypospadias, and long-term neurodevelopmental problems. A second trap is assuming risk disappears after the first trimester; neurodevelopmental effects relate to exposure across pregnancy, not only the early weeks. A third trap is assuming this only applies to the epilepsy indication; the same risk and the same regulatory restrictions apply when valproate is used for bipolar disorder.

Step 1, recognise the patient is of childbearing potential. Step 2: recall that valproate needs highly effective contraception and annual risk review under the Pregnancy Prevention Programme. Step 3: if pregnancy is confirmed or planned, involve specialist review before stopping or switching, since abrupt discontinuation risks seizure or mood relapse.