Pregnancy begins at the time of conception; this often cannot be determined exactly. Therefore, the calculation
of the weeks of pregnancy usually starts on the day of the last female cycle (i.e., the beginning of the last
menstrual period). In the second or third week of the cycle, ovulation
takes place (now the woman is ready to conceive). The egg remains capable of fertilization for 24 hours, male
sperm have a life span of 72 hours. If a sperm reaches an egg and penetrates its membrane, fertilization is
successful. The egg then travels through the fallopian tube into the uterus.