Does myasthenia gravis affect pregnancy?
Myasthenia gravis is an autoimmune neuromuscular disease characterized by weakness and fatigue of the skeletal muscles of the face and extremities. It affects people of both sexes and all ages, but twice as many female patients are affected as male patients. Myasthenia gravis usually strikes in women in their third decade of life.
Myasthenic crises (increased symptoms that lead to difficulty breathing) may occur during pregnancy. In other women, the disease may go into remission (complete or partial absence of symptoms). Pregnancy does not appear to hasten the progression of the disease. Pregnancy worsens myasthenia gravis in about one third of women, has no effect in one third, and improves symptoms in another third. About 12% of infants born to women with myasthenia gravis have "neonatal myasthenia," a temporary but potentially life-threatening condition. It is caused by the transfer of maternal antibodies into the fetal circulation just before birth. Symptoms include weakness, floppiness, feeble cry, and difficulty feeding. The infant may have difficulty breathing, requiring the use of a ventilator. Neonatal myasthenia usually clears up within a month.
Pregnant women with myasthenia gravis often have more weakness and fatigue because of the added weight and effort of pregnancy. Some pregnancy complications may be more likely in women with myasthenia gravis. Preterm labor (labor before 37 weeks of pregnancy) is more likely. It is thought that anticholinesterase medications used to treat myasthenia gravis may cause uterine contractions. Myasthenic crisis may be more likely during the stress of labor.
Delivery of the baby may be more difficult in women with myasthenia gravis. While labor itself is not affected by myasthenia gravis (the uterus is a smooth muscle), the muscles needed for pushing can be affected. This may make forceps and vacuum-assisted deliveries more likely.
A medication called magnesium sulfate that is commonly used for treating high blood pressure and preterm labor should not be used in women with myasthenia gravis. This drug blocks the nerve-muscle connections and can worsen myasthenia gravis muscle weakness.
Between 10 and 25 percent of babies born to women with myasthenia gravis may have neonatal myasthenia gravis. This occurs when antibodies common in myasthenia gravis cross the placenta to the developing fetus. These babies may be weak, with poor suck, and may have respiratory difficulty. Neonatal myasthenia gravis is usually temporary, lasting only a few weeks.