Diseases & Conditions
A premature newborn is a newborn delivered before 37 weeks in the uterus; such a newborn has underdeveloped organs.
About 8% of newborns are born prematurely (preterm). Many of these newborns are born just a few weeks early and do not experience problems related to their prematurity. However, the more prematurely newborns are born, the more they are prone to a number of serious and even life-threatening complications. Very premature birth is the single most common cause of death in the newborn. Also, newborns born very prematurely are at high risk for chronic problems, especially delayed development and learning disorders. Such disorders occur because the internal organs have not had time to develop adequately before birth.
The reason for a premature birth cannot usually be determined. However, the risk of premature birth is higher in women who are poor, have little education, and have poor nutrition or health or untreated illnesses or infections during pregnancy. The risk is lower in women who had early prenatal care. For unknown reasons, black women are significantly more likely than women of other racial groups to have a premature delivery. Other women at increased risk for premature delivery are those carrying more than one fetus and those who have serious or life-threatening disorders, including severe high blood pressure or kidney disease, preeclampsia or eclampsia (see Pregnancy Complications: Preeclampsia ), or infection of the uterus (chorioamnionitis).
Premature newborns usually weigh less than 5½ pounds. Physical features help doctors determine the newborn's gestational age (length of time spent in the uterus after the egg is fertilized).
Underdeveloped Lungs: The lungs of the premature newborn may not have had enough time to fully develop before birth. Such newborns are likely to have respiratory distress syndrome. Respiratory distress syndrome occurs if the lungs are not mature enough to produce surfactant, a mixture of lipids (fats) and proteins that allows the air sacs of the lungs to remain open (see Problems in Newborns: Respiratory Distress Syndrome ).
Underdeveloped Brain: The part of the brain that controls regular breathing may be so immature that the newborn has inconsistent breathing, with short pauses in breathing or periods during which breathing stops for 20 seconds or longer (apnea). The parts of the brain that control the mouth and throat are immature so the newborn cannot suck and swallow normally and will have difficulty coordinating feeding with breathing.
Brain Hemorrhage: Newborns born very prematurely are at increased risk of bleeding (hemorrhage) in the brain. Bleeding typically begins in an area called the germinal matrix and may extend into spaces within the brain called the ventricles. This form of hemorrhage is most likely to occur in those born very prematurely (before 32 weeks of pregnancy) and if there were problems during labor or delivery or breathing problems (such as respiratory distress syndrome) after birth. Depending on the size of the hemorrhage, newborns may have no symptoms or may experience lethargy, seizures, or even persistent unconsciousness (coma). Newborns with small or moderate-sized hemorrhages usually develop normally. Those with very large hemorrhages are at higher risk of dying or of having learning disorders or other brain-related problems later in life.
Abnormal Blood Sugar: Because premature newborns have difficulty maintaining normal blood sugar (glucose) levels, they are often treated with intravenous glucose solutions or given small frequent feedings. Without regular intake of sugar, a newborn may develop low blood sugar levels (hypoglycemia). Most newborns with hypoglycemia do not develop symptoms. Others may become listless with poor muscle tone, feed poorly, or become jittery. Rarely, seizures may develop. These newborns are also prone to developing high blood sugar levels (hyperglycemia) if they receive too much sugar intravenously. Most newborns with hyperglycemia do not develop symptoms.
Underdeveloped Immune System: Newborns who are born very prematurely have low levels of antibodies, which cross the placenta from mother to the fetus during the latter part of pregnancy and offer protection from infection. Therefore, the risk of developing infections, especially infection in the blood (sepsis), is higher in premature newborns. The use of special devices for treatment, such as catheters and ventilators, further increases the newborn's risk of developing serious infections.
Underdeveloped Kidneys: Before delivery, waste products produced in the fetus are removed by the placenta and then excreted by the mother's kidneys. After delivery, the newborn's kidneys must take over these functions. Kidney function is poor in newborns who are born very prematurely but improves as the kidneys mature. A newborn with underdeveloped kidneys is likely to have difficulty regulating the amount of salt and water in the body.
Underdeveloped Digestive Tract and Liver: Initially, premature newborns may have difficulty with feedings. Not only do they have immature sucking and swallowing reflexes, but also their small stomach empties slowly. Very premature newborns may develop a serious injury to the inner surface of the intestines (necrotizing enterocolitis (see Problems in Newborns: Necrotizing Enterocolitis ).
In premature newborns, the excretion of bilirubin may be impaired. Thus, premature newborns, even more than term newborns, tend to become jaundiced in the first few days after birth because of the build-up of bilirubin in their blood. Usually, the jaundice is mild and resolves as the newborn takes larger amounts of feedings and has more frequent bowel movements. Rarely, very high levels of bilirubin accumulate and put the newborn at risk for developing kernicterus, a form of brain damage caused by deposits of bilirubin in the brain.
Difficulty Regulating Body Temperature: Because premature newborns have a large skin surface area relative to their weight, they tend to lose heat rapidly, especially if they are in a cool room or if there is a draft. A lowering of body temperature results in a markedly increased rate of the body's metabolism, as the newborn attempts to maintain normal body temperature.
Physical Features of a Premature Newborn
Small size Large head relative to rest of the body Little fat under the skin Thin, shiny, pink skin Veins visible beneath the skin Few creases on soles of feet Scant hair Soft ears, with little cartilage Underdeveloped breast tissue Boys: Small scrotum with few folds. Testicles may be undescended in very premature newborns Girls: Labia majora not yet covering labia minora Rapid breathing with brief pauses (periodic breathing), often apnea spells (pauses lasting greater than 20 seconds) Weak, poorly coordinated sucking and swallowing reflexes Reduced physical activity (a premature newborn tends not to draw up the arms and legs as does a full-term newborn) Sleeping for most of the time
The best way for premature birth to be prevented is for the expectant mother to take good care of her own health. She should eat a nutritious diet and avoid cigarettes, alcohol, and drugs. Ideally, she should receive early and regular prenatal care so that any complications of pregnancy can be recognized and treated. If it seems probable that early labor is about to start, an obstetrician may administer drugs (such as magnesium sulfate or ritodrine Some Trade Names YUTOPAR ) to the mother to slow or stop contractions. Corticosteroids such as betamethasone Some Trade Names CELESTONE UTICORT VALISONE or dexamethasone Some Trade Names DECADRON HEXADROL may also be given to the mother to accelerate maturation of the fetus's lungs. Corticosteroids also significantly reduce the risk of brain hemorrhage if the newborn is born prematurely.
Treatment and Prognosis
Treatment involves managing the complications, such as respiratory distress syndrome and high bilirubin levels. Very premature newborns are fed intravenously until they can tolerate tube feedings and finally feedings by mouth. A premature newborn may need to be hospitalized for days, weeks, or months. Over recent decades, the survival of premature newborns has improved dramatically. For most premature newborns, the long-term prognosis is very good, and they develop normally. However, those born extremely early (often before 28 weeks of pregnancy) are at an increased risk of death and of serious problems, including mental retardation, cerebral palsy, epilepsy, or blindness. Fortunately, only a minority of extremely premature newborns who survive have these problems. A larger percentage have normal intelligence, but many have learning disorders that eventually require special help.
Last full review/revision February 2003
Source: The Merck Manual Home Edition