birth or labor, delivery of the fetus by the viviparous mammal. Birth is also known as parturition. Human birth normally occurs about 280 days after onset of the last menstrual period before conception.

The Stages of Labor

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.

Methods of Analgesia

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.

Natural Childbirth

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.

Complications of Childbirth

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 cesarean section (sĭzâr`ēən), delivery of an infant by surgical removal from the uterus through an abdominal incision.
..... Click the link for more information. . 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 erythroblastosis fetalis (ərĭth'rəblăstō`sĭs)
..... Click the link for more information. , 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 pregnancy pregnancy, period of time between fertilization of the ovum (conception) and birth , during which mammals carry their developing young in the uterus (see embryo ). The duration of pregnancy in humans is about 280 days, equal to 9 calendar months.
..... Click the link for more information. ; obstetrics obstetrics (ŏbstĕ`trĭks)
..... Click the link for more information. .

Bibliography

See D. Caton, What a Blessing She Had Chloroform (1999).

parturition

or birth or childbirth or labour or delivery

Process of bringing forth a child from the uterus, ending pregnancy. It has three stages. In dilation, uterine contractions lasting about 40 seconds begin 20–30 minutes apart and progress to severe labour pains about every 3 minutes. The opening of the cervix widens as contractions push the fetus. Dilation averages 13–14 hours in first-time mothers, less if a woman has had previous babies. When the cervix dilates fully, expulsion begins. The “water” (amniotic sac) breaks (if it has not already), and the woman may actively push. Expulsion lasts 1–2 hours or less. Normally, the baby's head emerges first; other positions make birth more difficult and risky. In the third stage, the placenta is expelled, usually within 15 minutes. Within six to eight weeks, the mother's reproductive system returns to nearly the prepregnancy state. See also cesarean section; lactation; midwifery; miscarriage; natural childbirth; obstetrics and gynecology; premature birth.

birth [bərth]

(biology)

The emergence of a new individual from the body of its parent.