Sperm are manufactured in the testes and ejaculated out through the vas deferens and urethra into the vagina. Then they begin their swim through the cervix and uterus and up a fallopian tube to meet the egg, which has already been released from the ovary. When the sperm and egg unite in the fallopian tube, conception occurs. The single fertilized egg cell then begins dividing as it travels down the tube, and finally it implants in the uterus. Various techniques for improving the chances of conception are available.

The placenta, which is important in transmitting substances between the woman and the fetus, develops early in pregnancy. The most remarkable development of the fetus occurs during the first trimester (first three months), when most of the major organ systems are formed and human features develop.

For the woman, early signs of pregnancy include amenorrhea, tenderness of the breasts, and nausea. The most common pregnancy tests are designed to detect hCG in the urine or blood. Physical changes during the first trimester are mainly the result of the increasing levels of estrogen and progesterone produced by the placenta. Despite cultural myths about the radiant contentment of the pregnant woman, some women do have negative feelings during the first trimester. During the second trimester the woman generally feels better, both physically and psychologically.

Despite many people's concerns, sexual intercourse is generally quite safe during pregnancy. Nutrition is exceptionally important during pregnancy because the woman's body has to supply the materials to create another human being. Pregnant women also must be very careful about ingesting drugs because some can penetrate the placental barrier and enter the fetus, possibly causing damage.

Labor is typically divided into three stages. During the first stage, the cervix undergoes effacement (thinning) and dilation. During the second stage, the baby moves out through the vagina. The placenta is delivered during the third stage. Cesarean section is a surgical method of delivering a baby.

The Lamaze method of "prepared" childbirth has become very popular; it emphasizes the use of relaxation and controlled breathing to control contractions and minimize the woman's discomfort. Anesthetics may not be necessary, which seems desirable, since they are potentially dangerous to the infant.

During the postpartum period, hormone levels are very low. Postpartum depression may arise from a combination of this hormonal state and the many environmental stresses on the woman at this time.

Two hormones are involved in lactation: prolactin and oxytocin. Breast-feeding has a number of psychological as well as health advantages.

Problems of pregnancy include ectopic (misplaced) pregnancy, pseudocyesis (false pregnancy), preeclampsia and eclampsia, illness (such as German measles), a defective conceptus, Rh incompatibility, spontaneous abortion, and preterm birth.

The most common cause of infertility in men and women is infection related to sexually transmitted diseases. New reproductive technologies include artificial insemination, frozen sperm banks, embryo transplants, in vitro fertilization (test-tube babies), and GIFT (gamete intrafallopian transfer), all of which are now a reality. These procedures are expensive and have low success rates.