Epilepsy complicates approximately 1 in 200 pregnancies. Convulsive disorders are the second most prevalent and certainly the most serious common neurological condition encountered in pregnant women.
The major pregnancy-related threats to women with epilepsy are increased seizure rates and risks to fetal malformations (see Chapter 8). Increased seizure frequency is often associated with subtherapeutic anticonvulsant levels, a lowered seizure threshold, or both. Subtherapeutic levels are caused by a variety of factors including (1) nausea and vomiting leading to skipped doses; (2) decreased gastrointestinal motility and the use of antacids, which reduce drug absorption; (3) expanded intravascular volume, which lowers serum drug levels; (4) the induction of hepatic, plasma, and placental enzymes that increase drug metabolism; and (5) increased glomerular filtration, which hastens drug clearance. These normal pregnancy changes are offset somewhat by the fact that decreased protein binding increases free drug levels. The threshold for seizures can also be affected by sleep deprivation and hyperventilation during labor. Women with the most severe epilepsy are more susceptible to increased seizure frequency during pregnancy.
A seizure is defined as a paroxysmal disorder of the central nervous system characterized by an abnormal neuronal discharge with or without a loss of consciousness. Epilepsy is defined as a condition characterized by a tendency for two or more recurrent seizures unprovoked by any known proximate insult.
These seizures originate in one localized area of the brain and affect a correspondingly localized area of neurological function. They are believed to result from a lesion caused by trauma, abscess, or tumor, although a specific lesion is rarely demonstrated. Simple motor seizures start in one region of the body and progress toward other areas of the same side, producing tonic and then clonic movements. Simple seizures can affect sensory function or produce autonomic dysfunction or psychological changes. Consciousness is usually not lost, and recovery is rapid. Partial seizures can secondarily generalize, producing loss of consciousness and generalized convulsions. Complex partial seizures, also called temporal lobe or psychomotor seizures, usually involve clouding of the consciousness and a feeling of disassociation or a dyscognitive state.
These seizures involve both hemispheres of the brain simultaneously, and may be preceded by an aura before an abrupt loss of consciousness. In grand mal seizures, loss of consciousness is followed by tonic contraction of the muscles and rigid posturing, and then by clonic contractions of all extremities while the muscles gradually relax. Loss of bowel or bladder control is common. Return to consciousness is gradual, and the patient may be confused and disoriented for some time.
Absence seizures, also called petit mal, involve a loss of consciousness without muscle activity, are very brief, and are characterized by immediate recovery of consciousness and orientation.
In general, the pregnant woman should receive the same evaluation as anyone else. Identifiable causes of convulsive disorders, including trauma, alcohol and other drug-induced withdrawal, brain tumors, arteriovenous malformations, and biochemical abnormalities, need to be ruled out. Both cranial computed tomography and magnetic resonance imaging are believed safe in pregnancy and should be utilized if needed.
Management is guided by specific goals before, during, and after pregnancy.
The offspring of epileptic women are at increased risk to have certain congenital malformations caused by epilepsy itself, the anticonvulsant medications, or a combination of both. The overall risk of major congenital malformations is increased 2.7-fold. Some seizure disorders are inheritable, and almost 10 percent of children develop a seizure disorder later in life. The specific drug-related risks are discussed in Chapter 8. Women taking antiepileptic medication should take 4 mg of folic acid per day as most of these agents deplete this nutrient.
The major goal of pregnancy management is to keep the woman seizure free. To accomplish this, she may need treatment for nausea and vomiting, she should avoid seizure-provoking stimuli, and compliance is urged for medication. In general, antiepileptic medication should be maintained at the lowest dose associated with seizure control. We recommend serum drug levels be measured only when seizures occur, or if noncompliance is suspected. Altered protein binding of anti-epileptic drugs during pregnancy makes standard values for therapeutic serum levels unreliable in pregnancy.
A pregnant woman with a new diagnosis of a seizure disorder should be started on antiepileptic medication. Treatment regimens depend on seizure classification. Please see Chapter 8, “Teratology, Medications, and Substance Abuse,” for treatment options.
A midpregnancy targeted ultrasound examination may identify fetal anomalies. Tests of fetal well-being might be indicated if there is poor fetal growth, inadequate seizure control, or comorbid maternal conditions.
Coadministration of oral contraceptives and anticonvulsants such as phenobarbital, primidone, phenytoin, and carbamazepine may cause breakthrough bleeding and contraceptive failure because anticonvulsants induce hepatic P450microsomal enzyme systems, increasing estrogen metabolism. Although an increased failure rate is speculative, many experts recommend that oral contraceptives containing 50 μg of estrogen be used in epileptic women taking anticonvulsants. Oral contraceptives are not associated with exacerbation of seizures. Anticonvulsants may adversely affect both male and fetal fertility.
For further reading in Williams Obstetrics, 23rd ed.,
see Chapter 55, “Neurological and Psychiatric Disorders.”