Myasthenia gravis is not inherited and it is not contagious. It generally develops later in life when antibodies in the body attack normal receptors on muscle. This blocks a chemical needed to stimulate muscle contraction. A temporary form of myasthenia gravis may develop in the fetus when a woman with myasthenia gravis passes the antibodies to the fetus. Generally, it resolves in 2 to 3 months.