A premature newborn is delivered before 37 weeks of development in the uterus. A premature newborn has underdeveloped organs, which may not be ready to function outside of the uterus.
Full-term pregnancy lasts 37 to 40 weeks. About 12% of newborns are born prematurely (preterm). Many of these newborns are born just a few weeks early and do not experience any problems related to their prematurity. However, the more prematurely newborns are born, the more they are prone to serious and even life-threatening complications. Extreme prematurity is the single most common cause of death in newborns. Also, newborns born very prematurely are at high risk of long-term problems, especially delayed development and learning disorders. Nonetheless, most infants who are born prematurely grow up with no long-term difficulties. The risk of premature birth is decreased with early prenatal care.
The reasons for premature birth are frequently unknown. However, the risk of premature birth is higher among adolescents and older women, women of lower socioeconomic status, women with inadequate prenatal care, and those with multiple fetuses (twins, triplets, quadruplets). Poor nutrition and untreated infections, such as urinary tract infections or sexually transmitted diseases, during pregnancy also increase the risk of premature birth. Other women at increased risk of premature birth are those who have had a previous premature birth or who themselves have serious or life-threatening disorders, including heart disease, severe high blood pressure, kidney disease, preeclampsia or eclampsia (see Complications of Pregnancy: Preeclampsia), or infection of the uterus (chorioamnionitis).
Premature newborns usually weigh less than 5½ pounds (2.5 kilograms), and some weigh as little as 1 pound (½ kilogram). An ultrasound examination of the fetus done early in the pregnancy and physical features and examination of the newborn after delivery help doctors determine the gestational age (length of time spent in the uterus after the egg is fertilized).
Symptoms often depend on immaturity of various organs. For example, some organs, such as the lungs or brain, may not be fully developed. Premature newborns may also have difficulty regulating their body temperature and the level of sugar in the blood. The immune system is also underdeveloped.
Risk of complications increases with increasing prematurity and depends in part on the presence of certain causes of prematurity, such as infection, diabetes, high blood pressure, or preeclampsia in the mother.
Several problems arise when an infant is born before the brain is fully developed. These problems include
Underdeveloped Digestive Tract and Liver:
An underdeveloped digestive tract and liver can cause several problems, including
Underdeveloped Immune System:
Infants born very prematurely have low levels of antibodies, substances in the bloodstream that help protect against infection. Antibodies cross the placenta (the organ that connects the fetus to the uterus and provides nourishment to the fetus) from mother to the fetus during the latter part of pregnancy. Therefore, the risk of developing infections, especially infection in the blood (sepsis), is higher in premature newborns. The use of special invasive devices for treatment, such as catheters in blood vessels and breathing (endotracheal) tubes, further increases the risk of developing serious infections.
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 diminished in very premature newborns but improves as the kidneys mature. Newborns with underdeveloped kidneys may have difficulty regulating the amount of salt and water in the body.
The lungs of premature newborns may not have had enough time to fully develop before birth. Such newborns are likely to have respiratory distress syndrome, causing visibly labored breathing, flaring of the nostrils while breathing in, a grunting sound while breathing out, and a bluish discoloration to the skin (cyanosis) if oxygen levels in the blood are low (see Problems in Newborns: Respiratory Distress Syndrome). Respiratory distress syndrome occurs if the lungs are not mature enough to produce surfactant, a substance that coats the inside of the air sacs and allows the air sacs of the lungs to remain open.
Difficulty Regulating Blood Sugar Levels:
Because premature newborns have difficulty feeding and maintaining normal blood sugar (glucose) levels, they are often treated with glucose (sugar) solutions given by vein (intravenously) or given small frequent feedings. Without regular feedings, newborns may develop low blood sugar levels (hypoglycemia—see see Hypoglycemia). Most newborns with hypoglycemia do not develop symptoms. Others become listless with poor muscle tone, feed poorly, or become jittery. Rarely, seizures develop. Premature newborns are also prone to developing high blood sugar levels (hyperglycemia) if they receive too much sugar intravenously, but hyperglycemia rarely causes symptoms.
Difficulty Regulating Body Temperature:
Because premature newborns have a large skin surface area relative to their weight compared to full-term newborns, they tend to lose heat rapidly and have difficulty maintaining normal body temperature, especially if they are in a cool room or if there is a draft. Therefore, their body temperature falls unless they are warmed in an incubator or by an overhead radiant warmer. If they are exposed to a cool environment, premature newborns generate extra body heat, markedly increasing their rate of metabolism and making it difficult for them to gain weight.
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, risk of death and long-term problems begins to increase in infants born before 26 weeks of pregnancy and particularly in those born before 24 weeks. Risks include delayed development, cerebral palsy, and vision impairment. Many newborns who are extremely premature have normal intelligence, but some have learning disorders that eventually require special help in school.
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 alcohol, tobacco, and drugs unless they are needed to treat a medical condition. Ideally, expectant mothers should receive early and regular prenatal care so that any complications of pregnancy can be recognized early and treated.
If labor starts well before term, obstetricians may give drugs to the pregnant woman to slow or stop contractions for a short time. During that interval, corticosteroids, such as betamethasone, may be given to the mother to speed the development of the fetus's lungs to reduce the risk of the newborn developing respiratory distress syndrome and also to reduce the risk of brain hemorrhage.
Treatment involves managing the complications of prematurity, such as respiratory distress syndrome and high bilirubin levels (hyperbilirubinemia). Very premature newborns are given nutrition into their veins until they can tolerate feedings into their stomach through a feeding tube and eventually feedings by mouth. The mother's breast milk is the best food for premature infants. Use of breast milk decreases the risk of developing necrotizing enterocolitis. Premature newborns may need to be hospitalized for days, weeks, or months.
Last full review/revision February 2009 by Arthur E. Kopelman, MD