Onset of labor, the first stage, is heralded by contractions of the uterus felt as cramplike pains in the abdomen or lower back that recur at intervals of 10 to 30 minutes and last about 40 seconds; they increase in frequency until they occur at about 2-minute intervals. With each contraction the cervix, or neck of the uterus, dilates until it becomes wide enough, about 4 in. (10 cm), to permit emergence of the baby.
In the second stage of labor the baby passes through the birth canal, most commonly head first, and is born. The effectiveness of uterine contractions in this stage is enhanced by the bearing-down abdominal contractions of the mother.
The third stage of labor, which occurs about 15 to 30 minutes after the child is born, is characterized by the separation of the placenta from the uterine wall and its expulsion. The total time of labor averages 13 to 14 hours in women pregnant for the first time and 8 to 9 hours in women who have previously borne children.
The pain of childbirth can be relieved with a variety of analgesic and sedative drugs, including morphine, barbiturates, and chloroform. However, many drugs that relieve pain also slow the uterine contractions or dangerously depress the baby's respiratory system. Spinal anesthetics, injected directly into the spinal cord, while not dangerous to the child, are difficult to administer accurately and are therefore potentially dangerous to the mother. Hypnosis has also been used experimentally.
In recent years so-called natural childbirth has come into wide use; the advantages are that the child is born undrugged and the mother can be conscious at the moment of birth. Natural childbirth emphasizes the ability of many women to give birth with a minimal amount of pain-killing drugs or none at all. The Dick-Read method, formulated by the British obstetrician of that name, emphasizes maternal understanding of the birth process as an aid to relaxation, and exercises to strengthen muscles and encourage proper breathing. The Lamaze method, or psychoprophylaxis, is of Russian origin; it uses breathing exercises as a conditioned response to uterine contractions.
Birth often cannot proceed normally because of a defect of the cervix or weak uterine contractions; breech births, in which the feet or buttocks emerge first, and transverse births, in which the child is positioned across the uterus, usually require obstetrical intervention, such as forceps delivery, manually turning the baby, or performing a cesarean section. About 10% of pregnancies terminate in deliveries that are too early, producing (after at least 200 days of gestation) premature infants requiring special care. Birth of a fetus prior to about 200 days of gestation is termed a miscarriage; birth within the first three months, an abortion. Stillbirth is the delivery of a dead child.
Complications of childbirth affecting the newborn include infant blindness attributable to gonorrhea infection, now largely eliminated by routine administration of silver nitrate to the eyes; retrolental fibroplasia, a type of blindness common for some years in premature infants that was found to result from administration of high concentrations of oxygen and is now largely avoided; and erythroblastosis fetalis, or Rh disease, which can often be prevented. Puerperal fever, an infection of the mother's genital tract once common following labor and delivery, has now also been largely eliminated by preventive hygiene, especially in labor, and by antibiotic therapy.
See D. Caton, What a Blessing She Had Chloroform (1999).
Two words used to describe human offspring while in utero are embryo and fetus. Their meanings refer to earlier and later stages of development. Amphibians under go symbiosis before they lay their eggs and metamorphosis after.