a. The length of pregnancy varies greatly.

Nevertheless, the normal duration of pregnancy is about 9 1/2 to 10 months (lunar), 38 to 40 weeks.

b. It is usually not possible to determine the actual time of fertilization because reliable records concerning sexual activities are seldom available. However, the approximate time can be calculated.

c. The estimated date of confinement (EDC) is calculated as follows:

(1) The first day of last menstrual period.

(2) Count back 3 months.

(3) Add seven days.

(4) Add one year.