Myasthenia Gravis and Pregnancy

What is myasthenia gravis?

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Myasthenia gravis (MG) is a complex autoimmune disorder in which antibodies destroy neuromuscular connections. This results in muscle weakness and fatigue. The Myasthenia Gravis Foundation estimates the incidence of MG in the United States to be about 20 out of 100,000 and, at younger ages, occurs in women more often than men. The degree of muscle weakness depends on the severity of the disease. Weakness occurs in the muscles under voluntary control, especially in the eyes, mouth, throat, and limbs.

Myasthenia gravis is diagnosed by various tests for muscle strength and nerve conduction. Treatment varies greatly among individuals depending on the severity of the disease, but may include steroid medications and immunosuppressant drugs. Many people with MG have a thymectomy, surgery to remove the thymus which is a gland located under the breastbone. Although MG improves in some people after thymectomy, the role of the thymus in MG is not fully understood.

How does pregnancy affect myasthenia gravis?

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.

How does myasthenia gravis affect pregnancy?

Pregnant women with MG 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 MG. Preterm labor (labor before 37 weeks of pregnancy) is more likely. It is thought that anticholinesterase medications used to treat MG 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 MG. While labor itself is not affected by MG (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 MG. This drug blocks the nerve-muscle connections and can worsen MG muscle weakness.

Between 12 and 20 percent of babies born to women with MG may have neonatal myasthenia gravis. This occurs when antibodies common in MG cross the placenta to the developing fetus. These babies may be weak, with poor suck, and may have respiratory difficulty. Neonatal MG is usually temporary, lasting only a few weeks.

Management of myasthenia gravis during pregnancy

Pregnant women with MG need close monitoring of the disease. More frequent prenatal visits are often needed.

Management of pregnancy with myasthenia gravis may include the following:

• Adjustment of medication type and dosage

• Avoiding emotional and physical stress

• Monitoring for signs of myasthenic crisis

• Ultrasound--a diagnostic imaging technique which uses high-frequency sound waves and a computer to create images of blood vessels, tissues, and organs. Ultrasounds are used to view internal organs as they function, and to assess blood flow through various vessels used to monitor fetal growth and development.

• Fetal monitoring (for signs of muscle weakness that may indicate fetal MG)

• Other fetal testing including Doppler flow studies (to monitor the blood flow in the uterus and umbilical cord)

Women with myasthenia gravis can increase their chances for a healthy pregnancy by getting early prenatal care and working with their health care providers in the management of their disease.