Premature, << `pree` muh CHUR, >> birth occurs when a woman gives birth to a baby before the end of the normal period of pregnancy. The normal period of pregnancy ranges from 37 to 41 weeks after a woman begins her last menstrual period prior to becoming pregnant. Births that take place before the end of 37 weeks of pregnancy are said to occur preterm.
Most premature infants that weigh more than 31/3 pounds (1.5 kilograms) at birth grow up as healthy as babies born after a normal pregnancy. Premature babies weighing less than 21/5 pounds (1 kilogram) at birth have the poorest chance of survival.
In many premature infants, certain organs—especially the lungs—have not developed sufficiently for the baby to survive without medical assistance. Respiratory distress syndrome, also called hyaline membrane disease, ranks among the most serious lung disorders that strike these babies. Some infants with this condition are attached to a respirator. See Respiratory distress syndrome . Other common problems include the inability to digest normal-sized feedings and the body’s lack of adequate control over its temperature. If the baby can suck and swallow, special formulas may be given by bottle. Some premature infants must be fed by means of a tube passed through the nose and into the stomach. Others may need to be fed entirely through a tube inserted into a blood vessel. Most premature infants are placed in an incubator to assure a constant body temperature. See Incubator (Hospital incubators) .
Premature births occur least often among healthy women who receive periodic medical care. A woman can help assure normal birth by eating a well-balanced diet and by avoiding the use of tobacco, alcohol, and all drugs except those recommended by her doctor. In the United States, about 7 percent of white babies and 14 to 15 percent of nonwhite babies are born prematurely.
The causes of preterm births are poorly understood. Factors involved include conditions in the mother, the baby, and the placenta. The placenta is an organ that develops during pregnancy, joining the mother and the unborn baby. Many women have a medical condition associated with premature birth. Such conditions include abnormalities of the uterus, drug addiction, high blood pressure, and being pregnant with more than one baby. A woman who has had a premature baby or a miscarriage has about a 20 percent chance of again giving birth prematurely. Scientists have developed a number of drugs that can help stop preterm labor before it results in premature birth.
See also Neonatology ; Preeclampsia .
