Unusually for autoimmune diseases, there is no evidence that myasthenia gravis is typically inherited. However, pregnant women—and women who are considering becoming pregnant—who have the condition need to be aware of the risks, both to themselves and to their fetuses. Women under 40, who are in their childbearing years, are particularly at risk for myasthenia gravis.
About one in three pregnant women with myasthenia gravis report their symptoms getting worse, mostly in the first trimester. In some women, it heightens the risk of myasthenic crisis, a dangerous condition in which the pulmonary muscles are too weak for the patient to continue breathing. It is difficult to predict how pregnancy will affect the course of the disease in a particular patient, however; in some cases, in fact, women experience a remission, and are symptom-free during pregnancy. Most women have few myasthenia symptoms in the second and third trimesters.
Preeclampsia—a condition in which a pregnant woman has high blood pressure and protein in the urine, and which often results in induced labor and premature delivery—is more common in expectant mothers with autoimmune diseases, including myasthenia. The most common treatment for preeclampsia is magnesium sulphate used to induce labor, but it is unsafe for myasthenia patients; if it develops into seizures, the drug Dilantin is used.
Pregnant women may need to avoid the medications used for myasthenia. Immunosuppressants can be particularly dangerous for a developing fetus. While another type of medication called cholinesterase inhibitors are usually safe, when taken intravenously, these drugs can cause premature labor. On the other hand, corticosteroids such as prednisone are believed to be safe for mother and fetus alike.
In about one case in five, the baby will be born with neonatal myasthenia gravis. This is not inherited, but comes from the mother’s antibodies being transferred through the placenta. It varies in severity from infant to infant, but it can be safely treated with cholinesterase inhibitors and usually goes away within a few weeks. In other cases, these antibodies affected fetal movement, leading to a rare joint deformity disorder called arthrogryposis. This does not affect cognitive function, however, nor does it get worse over time.
If you are pregnant, or want to be, and have myasthenia, be sure to let you OB/GYN know. They can work with you to help keep you and your baby safe and healthy.