Assume that the mean length of a human pregnancy is 268 days with a standard deviation of 9 days. what percentage of human pregnancies do we expect to last no more than 260 days?

  The average time of pregnancy is 268 days (38 weeks and two days) from ovulation, with a standard deviation of 10 days or a coefficient of variation of 3.7%. Gestational age is calculated from the first day of the woman's last normal menstrual cycle.

  However, only 5% of births occur on the expected date of delivery and at the age of 40 weeks of gestation. 50% of births occur one week before or one week after the expected date. 80% occurs between two weeks before or after