Prematurity and perinatal mortality in the Rhesus (Macaca mulatta): relationship to birth weight and gestational age.

While the relative influence of birth weight and gestational age in determining perinatal mortality has not been definitively established, it has been assumed that birth weight makes the predominant contribution to perinatal mortality. The joint effects of birth weight and gestational age were examined by analyzing approximately 2,500 births from timed pregnancies in two rhesus (Macaca mulatta) breeding colonies. Perinatal events in the rhesus are described and shown to be similar to the human. The results demonstrate that gestational age is as important as birth weight in determining perinatal mortality. Since the degree of accuracy in the estimation of rhesus gestational age was much greater than is usually attained in human studies, the estimation of gestational age from the last menses may be too crude to determine the importance of this variable in human perinatal mortality.