Pathology of perinatal hypoxia.

At birth the newborn infant is required to make an abrupt adjustment to a new environment. The most immediate changes required to support extrauterine life are concerned with respiration and the circulation. The infant must be able to expand its lungs fully and at the same time the pulmonary circulation must be adequate for gaseous exchange to occur between the air spaces and the pulmonary capillaries. Even the mature infant may have some difficulty in making the adjustment and this becomes an even greater problem in the case of the premature baby. In many instances there may be no apparent cause for the interruption of the pregnancy and the infant is inherently healthy but is under 2500g birthweight. In some pregnancies, however, maternal factors such