• parturition;
  • menstrual cycle;
  • fetal biparietal diameter


Accurate assessment of gestational age, date of parturition, and evaluation of placental abnormalities are essential to monitor obstetrical and fetal complications in captive chimpanzee (Pan troglodytes) breeding colonies. Since ultrasonography is a safe and noninvasive technique for monitoring chimpanzee pregnancies, we have developed a technique to estimate the date of parturition using the fetal biparietal diameter (BPD) of the skull from real-time ultrasonographic measurements. A formula for determining gestational age was based on analysis of data obtained from 62 pregnancies over an 8-year period. From this formula an estimated gestational age was calculated and compared with menstrual cycle data from the period near the time of the estimated date of conception (EDC). If the data from the scan and cycle history were in agreement within 7 days, the estimate date of conception was corrected to be 3 days prior to detumescence of the sex cycle phase. Lastly, the estimated date of parturition (EDP) was predicted to be 240 days after the EDC. To evaluate the utility of this prediction, we subsequently examined 13 chimpanzee pregnancies using the above technique and compared it to the actual date of parturition (ADP). Nine of the 13 chimpanzees delivered within 2 weeks of the EDP. In addition to estimating gestational age, ultrasonography may be a useful tool for evaluating fetal growth and placental abnormalities and assessing third trimester complications in chimpanzee pregnancies.