The U.S. Food and Drug Administration (FDA) has labeled zonisamide as "Pregnancy Category C" and recommends that women who could possibly become pregnant should use effective birth control while using zonisamide. Recognizing that seizures in the mother also may be hazardous to a fetus, however, they conclude that the risks and benefits must be weighed in considering the use of Zonegran during pregnancy. Tell your doctor right away if you are pregnant or thinking about becoming pregnant.

The use of zonisamide by pregnant women hasn't been fully studied, but there are serious concerns based on studies using animals. When it was given to pregnant mice, rats, and dogs early in pregnancy, there were high rates of fetal abnormalities, especially heart defects and skeletal malformations. After it was given to monkeys during certain stages of pregnancy, many of the fetuses died, possibly because of malformations. All of these effects occurred at doses (and blood levels in the mother) that were equivalent to the amounts used to treat epilepsy in humans, or sometimes even lower. There was also a higher rate of death among the offspring of rats who were given zonisamide late in their pregnancy.

In one study in Japan of 26 human pregnancies, there were 2 malformations affecting fetuses whose mothers were receiving zonisamide along with other seizure medicines, but none among 4 whose mothers were receiving only zonisamide. Based on this information, the researchers suggested that the risk may not be greater than for other seizure medicines, but such risk "cannot be neglected," especially if more than one medicine is being used. In general, the risk of birth defects is higher for women who take more than one seizure medicine and for women with a family history of birth defects.

Women who are capable of becoming pregnant should take at least 400 mcg (0.4 mg) of folic acid (folate) daily to help prevent a type of birth defect called a neural tube defect. (The best-known of these is spina bifida, in which the spinal cord is not completely enclosed.) Women at high risk, such as those with a history of this kind of defect in a previous pregnancy, should take 4000 mcg (4 mg) daily, beginning before they become pregnant.

About 20% to 35% of women have seizures more often during pregnancy because of changes in hormones or changes in how their seizure medicine is handled by the body. While this may not be a particular problem for zonisamide, the doctor may recommend checking the level of medication in the blood regularly during pregnancy so that the dosage can be adjusted as needed.

It is not known whether zonisamide is found in human milk, but because of the possibility that it may have effects on the baby, zonisamide should be used during breast-feeding only after weighing the benefits against the risks. Talk to your doctor about whether you should stop nursing or stop taking zonisamide.

Studies in rats showed decreases in fertility when zonisamide was given. Its effect on human fertility is unknown.

The effect on labor and delivery also is unknown.