Control data on pre- and neonatal survival of captive chimpanzees.

Colony breeding records were analyzed in order to obtain information on pre- and neonatal survival in chimpanzees. Biweekly urinary chorionic gonadotrophin testing appeared suitable for determining pregnancy age. The probability of pregnancy termination was low (0.008 per 10 days) to a pregnancy age of 180 days. Between the ages of 180-210 days it was 0.080 per 10 days, and it steadily increased to one per 10 days after 240 days of age. There were no livebirths before 190 days of pregnancy age. Thereafter, the probability of a delivery to be a livebirth rapidly increased to about 0.90 after 210 days of pregnancy age. Infant mortality was less than 0.026 during the first two years of life.