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21 weeks or less: 0 percent survival rate
22 weeks: 0 to 10 percent survival rate
23 weeks: 10 to 35 percent survival rate
24 weeks: 40 to 70 percent survival rate
25 weeks: 50 to 80 percent survival rate
26 weeks: 80 to 90 percent survival rate
27 weeks: greater than 90 percent survival rate
According to the March of Dimes Foundation, there were 480,812 births in the United States in 2002 that occurred before 37 weeks gestation. This number represents 12.1 percent of live births that year. In an average week, approximately 9,200 infants are born prematurely, and approximately 1,500 are born before 32 weeks gestation. Black infants have the highest prematurity rate with 17.6 percent of live births; Native American (12.9%); Hispanic infants (11.4%); white infants (10.7%); and Asian infants (10.2%). Mothers younger than 20 years of age or older than 35 years of age have higher rates of preterm delivery.
Respiratory distress syndrome (RDS) is the most common problem in premature infants. Babies born too soon have immature lungs that have not developed surfactant, a protective film that helps air sacs in the lungs to stay open. With RDS, breathing is rapid and the center of the chest and rib cage pull inward with each breath. Extra oxygen can be supplied to the infant through tubes that fit into the nostrils of the nose or by placing the baby under an oxygen hood. In more serious cases, the baby may have to have a breathing tube inserted and receive air from a respirator or ventilator. A surfactant drug can be given in some cases. Extra oxygen may be needed for a few days or weeks. Bronchopulmonary dysplasia is the development of scar tissue in the lungs and can occur in severe cases of RDS.
Necrotizing enterocolitis (NEC) is another complication of prematurity. In this condition, part of the baby"s intestine is destroyed as a result of bacterial infection. In cases where only the innermost lining of the bowel dies, the infant"s body can regenerate it over time; however, if the full thickness of a portion dies, it must be removed surgically and an opening (ostomy) must be made for the passage of wastes until the infant is healthy enough for the remaining ends to be sewn together. Because NEC is potentially fatal, doctors are quick to respond to its symptoms, which include lethargy, vomiting, a swollen and/or red abdomen, fever, and blood in the stool. Measures include taking the infant off mouth feedings and feeding him or her intravenously, administering antibiotics, and removing air and fluids from the digestive tract via a nasal tube. Approximately 70 percent of NEC cases can be successfully treated without surgery.
Intraventricular hemorrhage (IVH) is another serious complication of prematurity. It is a condition in which immature and fragile blood vessels within the brain burst and bleed into the hollow chambers (ventricles) normally reserved for cerebrospinal fluid and into the tissue surrounding them. Physicians grade the severity of IVH according to a scale of I through IV, with I being bleeding confined to a small area around the burst vessels and IV being an extensive collection of blood in the ventricles and in the brain tissue itself. Grades I and II are not uncommon, and the baby"s body usually reabsorbs the blood with no ill effects. However, more severe IVH can result in hydrocephalus, a potentially fatal condition in which too much fluid collects in the ventricles, exerting increased pressure on the brain and causing the baby"s head to expand abnormally. To drain fluid and relieve pressure on the brain, doctors either perform lumbar punctures, a procedure in which a needle is inserted into the spinal canal to drain fluid; install a reservoir, a tube that drains fluid from a ventricle and into an artificial chamber under or on top of the scalp; or install a ventricular shunt, a tube that drains fluid from the ventricles and into the abdomen, where it is reabsorbed by the body. Infants who are at high risk for IVH usually have an ultrasound taken of their brain in the first week after birth, followed by others if bleeding is detected. IVH cannot be prevented; however, close monitoring can ensure that procedures to reduce fluid in the brain are implemented quickly to minimize possible damage.
Apnea of prematurity is a condition in which the infant stops breathing for periods lasting up to 20 seconds. It is often associated with a slowing of the heart rate. The baby may become pale, or the skin color may change to a blue or purplish hue. Apnea occurs most commonly when the infant is asleep. Infants with serious apnea may need medications to stimulate breathing or oxygen through a tube inserted in the nose. Some infants may be placed on a ventilator or respirator with a breathing tube inserted into the airway. As the baby gets older, and the lungs and brain tissues mature, the breathing usually becomes more regular. A group of researchers in Cleveland reported in 2003, however, that children who were born prematurely are three to five times more likely to develop sleep-disordered breathing by age 10 than children who were full-term babies.
As the fetus develops, it receives the oxygen it needs from the mother"s blood system. Most of the blood in the infant"s system bypasses the lungs. Once the baby is born, its own blood must start pumping through the lungs to get oxygen. Normally, this bypass duct closes within the first few hours or days after birth. If it does not close, the baby may have trouble getting enough oxygen on its own. Patent ductus arteriosus is a condition in which the duct that channels blood between two main arteries does not close after the baby is born. In some cases, a drug called indomethacin can be given to close the duct. Surgery may be required if the duct does not close on its own as the baby develops.
Retinopathy of prematurity is a condition in which the blood vessels in the baby"s eyes do not develop normally, and can, in some cases, result in blindness. Premature infants are also more susceptible to infections. They are born with fewer antibodies, which are necessary to fight off infections.
Physicians cannot predict long-term complications of prematurity; some consequences may not become evident until the child is school age. Minor disabilities like learning problems, poor coordination, or short attention span may be the result of premature birth but can be overcome with early intervention. The risks of serious long-term complications depend on many factors, including how premature the infant was at birth, the weight at birth, and the presence or absence of breathing problems. Gender is an associated factor: a Swedish study published in 2003 found that boys are at greater risk of death or serious long-term consequences of prematurity than girls. For example, 60 percent of boys born at 24 weeks" gestation die compared to 38 percent mortality for girls. The development of infection or the presence of a birth defect can also affect long-term prognosis. Infants who have infections in prematurity and very low birth weight are at risk for later disorders of the nervous system; a study done at Johns Hopkins reported that 77 out of a group of 213 premature infants developed neurologic disorders. Severe disabilities such as brain damage, blindness, and chronic lung problems are possible and may require ongoing care.
