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).
Birth less than 37 weeks after conception. Infants born as early as 23–24 weeks may survive but many face lifelong disabilities (e.g., cerebral palsy, blindness, deafness). Premature infants account for 8–9percnt of live births but two-thirds of infant deaths. 40–50percnt of cases have no explanation; other cases can be attributed to such causes as maternal hypertension or diabetes, multiple pregnancy, or placental separation. With good care, about 85percnt of live-born premature infants should survive. Infants born very early (before 32–34 weeks) lack fully developed lungs and often develop respiratory distress syndrome. They also have problems maintaining body temperature and fighting infection. Most deaths result from breathing problems, infections, and brain or lung hemorrhages. Premature infants are characterized by low birth weight, small size, irregular breathing, absence of subcutaneous fat, and thin skin.
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Birth of more than one child from one pregnancy. Twins are most common, born in 1 of about every 80 pregnancies. Identical twins develop from a single fertilized egg, which splits into two genetically identical embryos (though physical traits may be modified during their development); they occur randomly but are more likely in older mothers. Incomplete or late division results in conjoined twins. Fraternal twins develop from two eggs fertilized by two sperm and are no more genetically alike than are other siblings. Most common among persons of African ancestry and least common among those of Asian ancestry, fraternal twins seem to run in families. Repeated twinning produces triplets, quadruplets, and so on; these multiples may be identical, fraternal, or a combination. The use of fertility drugs has increased the number of high-order multiple births. Medical and psychological “twin studies” compare fraternal and identical twins to learn about genetic influences on various characteristics and diseases.
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A large group of disorders arising during development that cause abnormality of the human body. Most are due to genetic factors such as inherited or spontaneous mutations, whereas others are caused by environmental influences during pregnancy such as exposure to harmful chemicals. The most severe and lethal disorders arise during the first 28 days of development and include gross brain anomalies and heart defects. The mildest malformations occur in the late stages of development and are often the result of dominant inheritance, whereas complex congenital syndromes are often the result of recessive inheritance. Seealso birth defect; Down syndrome.
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Voluntary limiting of human reproduction, using such means as contraception, sexual abstinence, surgical sterilization, and induced abortion. The term was coined in 1914–15 by Margaret Sanger. Medically, birth control is often advised when childbirth might endanger the mother’s health or substantial risk exists of bearing a severely disabled child. Socially and economically, limitation of reproduction frequently reflects a desire to maintain or improve family living standards. Most religious leaders now generally agree that some form of fertility regulation is desirable, though the means are strongly debated. Seealso family planning.
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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. Seealso cesarean section; lactation; midwifery; miscarriage; natural childbirth; obstetrics and gynecology; premature birth.
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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.