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Epilepsy is the commonest neurological disorder encountered in pregnancy affecting 0.5% of pregnant women. The main issues are possible teratogenicity associated with anticonvulsants and adjustment of doses of drug to control fits. The incidence of congenital malformations in children of mothers with epilepsy is about 3–5% which is three times higher than in the general population. In part, this could reflect a genetic predisposition, but anticonvulsants seem largely to be responsible. Most evidence exists for the older drugs: carbamazepine, phenytoin and valproate, with cleft palate, neural tube defects and congenital heart disease being the most common findings. Sodium valproate is associated with a 40% risk of persistent neurodevelopmental disorders and 10% risk of birth defects during pregnancy. It should be avoided in women of childbearing age unless there are compelling indications. There is much less evidence for the newer anticonvulsant drugs but preliminary data suggest low rates of malformations (Table 1.9), particularly with lamotrigine and oxcarbazepine. There is a dose–response relationship for valproate (>1 g/day) and lamotrigine (>400 mg/day). Co‐administration of anticonvulsants produces a greater risk than when either drug is used alone (Table 1.10). To increase our knowledge of the effects of epilepsy and its drug treatment on pregnancy, all women should be added to the UK epilepsy and pregnancy register. The key points to managing pregnant women with epilepsy are shown in the Key point box in this section.

The pharmacokinetic changes associated with pregnancy are clinically important in the treatment of epilepsy. There are several factors in pregnancy which influence drug levels including altered protein binding, changes in absorption, increased plasma volume, and increased metabolism and excretion. Non‐compliance is also an issue in mothers concerned about the effects of the drugs. Therapy should be monitored by the clinical response and seizure activity and the lowest effective dose should be used. Generally, dose increases are required in pregnancy particularly for drugs with little protein binding such as lamotrigine which may need to be increased two‐ to threefold. After delivery, if drugs were increased during pregnancy, they should be reduced to preconception levels by around 1 week post‐partum. Breastfeeding should be encouraged as most anticonvulsants are secreted in very small amounts in breast milk. Neonates should be monitored for sedation. Higher doses of oestrogen in the combined oral contraceptive pill and progesterone in progesterone‐only contraception are required in women on hepatic enzyme‐inducing drugs.

Table 1.9 Data from UK epilepsy and pregnancy register 2005.

Anticonvulsant	Major malformation rate (%)
Carbamazepine	2.2
Sodium valproate	6.2
Lamotrigine	3.2
Phenytoin	3.7

Table 1.10 Influence of anti‐epileptic drug treatment on rates of congenital malformations.

	Major congenital malformation rate (%)
No anti‐epileptic drug	3.5
Monotherapy	3.7
Polytherapy	6.0