Premature birth occurs in 30 or 35 per cent of the cases of broken compensation in heart disease . The premature infants are, in these cases, often imperfectly nourished as a result of the poor aeration of the mother's blood. Exophthalmic goiter is occasionally the cause of premature emptying of the uterus. If chronic dyspnea exists, as a result of laryngeal or tracheal stenosis from pressure, the development of the fetus will necessarily be retarded. Any of the acute infectious diseases may be responsible for the termination of pregnancy before the end of term.
Premature labor is very common in pneumonia and influenza, being more frequent in late pregnancy.
Of local conditions , diseases of the decidua or endometrium, gonorrheal infection and malpositions of the uterus frequently result in premature labor, but usually before the fetus is viable. Anomalous positions of the fetus in utero may be responsible for the premature expulsion of the uterine contents. The occurrence of multiple pregnancy is a fruitful source of premature labor. About 70 per cent of twin pregnancies terminate prematurely and the length of practically all triplet and quadruplet gestations is considerably shortened in most cases due to lack of room in the uterine cavity. Even when mature, twins are usually small and of low body weight.