They can be sexed by examining the genitalia. The gestation is varying from 140-146 days. A few weeks before giving birth they become less active. Do not disturb them when giving birth. Normally it take place at night.
Labour takes about one hour.
Labour being calculated from the time contractions were first visible to the first young. The interval between infants usually is 2-5 minutes. The afterbirth normally follows 10-30 minutes after the birth of the last young, and is eaten by the female and other group members. They usually give birth to twins. Sometimes 1 or 3 monkeys are born.