The length of a normal pregnancy or gestation is considered to be 40 weeks (280 days) from the date of conception. Infants born before 37 weeks gestation are considered premature and may be at risk for complications.
More than one out of every ten infants born in the United States is born prematurely. Advances in medical technology have made it possible for infants born as young as 23 weeks gestational age (17 weeks premature) to survive. These premature infants, however, are at higher risk for death or serious complications, which include heart defects, respiratory problems, blindness, and brain damage.
Causes & Symptoms
The birth of a premature baby can be brought on by several different factors, including premature labor; placental abruption, in which the placenta detaches from the uterus; placenta previa, in which the placenta grows too low in the uterus; premature rupture of membranes, in which the amniotic sac is torn, causing the amniotic fluid to leak out; incompetent cervix, in which the opening to the uterus opens too soon; and maternal toxemia, or blood poisoning. While one of these conditions are often the immediate reason for a premature birth, its underlying cause is usually unknown. Prematurity is much more common in multiple pregnancy and for mothers who have a history of miscarriages or who have given birth to a premature infant in the past. One of the few, and most important, identifiable cause of prematurity is drug abuse, particularly cocaine, by the mother.
Infants born prematurely may experience major complications due to their low birth weight and the immaturity of their body systems. Some of the common problems among premature infants are jaundice (yellow discoloration of the skin and whites of the eyes), apnea (a long pause in breathing), and inability to breast or bottle feed. Body temperature, blood pressure, and heart rate may be difficult to regulate in premature infants. The lungs, digestive system, and nervous system (including the brain) are underdeveloped in premature babies, and are particularly vulnerable to complications. Some of the more common risks and complications of prematurity are described below.
Respiratory distress syndrome (RDS) is the most common problem seen 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 to coat the lung tissue. Extra oxygen may be need for a few days or weeks, depending on how small and premature the baby was at birth. Bronchopulmonary dysplasia is the development of scar tissue in the lungs, and can occur in severe cases of RDS.
Necrotizing enterocolitis (NEC) is a further complication of prematurity. In this condition, part of the baby's intestines are 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 (ostemy) 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% 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-IV, with I being bleeding confined to a small area around the burst vessels and IV being an extensive collection of blood not only in the ventricles, but in the brain tissue itself. Grades I and II are not uncommon, and the baby's body usually reabsorbs the blood with not 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 will either perform lumbar punctures, a procedure in which a needle is inserted into the spinal canal to drain fluids; 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 where 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.
As the fetus develops, it gets 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 where the duct that channels blood between two main arteries does not close after the baby is born. In some cases, a drug, indomethacin, can be given to close the duct. Surgery may be required, however, the duct may close on its own as the baby develops.
Retinopathy of prematurity is a condition where 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.
Many of the problems associated with prematurity depend on how early the baby is born and how much it weighs at birth. The most accurate way of determining the gestational age of an infant in utero is calculating from a known date of conception or using ultrasound imaging to observe development. When a baby is born, doctors can use the Dubowitz exam to estimate gestational age. This standardized test scores responses to 33 specific neurological stimuli to estimate the infant's neural development. Once the baby's gestational age and weight are determined, further tests and electronic fetal monitoring may need to be used to diagnose problems or to track the baby's condition. A blood pressure monitor may be wrapped around the arm or leg. Several types of monitors can be taped to the skin. A heart monitor or cardiorespiratory monitor may be attached to the baby's chest, abdomen, arms, or legs with adhesive patches to monitor breathing and heart rate. A thermometer probe may be taped on the skin to monitor body temperature. Blood samples may be taken from a vein or artery. X rays or ultrasound imaging may be used to examine the heart, lungs, and other internal organs.
Treatment depends on the types of complications that are present. It is not unusual for a premature infant to be placed in a heat-controlled unit (an incubator) to maintain its body temperature. Infants that are having trouble breathing on their own may need oxygen either pumped into the incubator, administered through small tubes placed in their nostrils, or through a respirator or ventilator which pumps air into a breathing tube inserted into the airway. The infant may require fluids and nutrients to be administered through an intravenous line where a small needle is inserted into a vein in the hand, foot, arm, leg, or scalp. If the baby needs drugs or medications, they may also be administered through the intravenous line. Another type of line may be inserted into the baby's umbilical cord. This can be used to draw blood samples or to administered medications or nutrients. If heart rate is irregular, the baby may have heart monitor leads taped to the chest. Many premature infants require time and support with breathing and feeding until they mature enough to breath and eat unassisted. Depending on the complications, the baby may require drugs or surgery.
Advances in medical care have made it possible for many premature infants to survive and develop normally. However, whether or not a premature infant will survive is still intimately tied to his or her gestational age:
- 21 weeks or less: 0% survival rate
- 22 weeks: 0-10% survival rate
- 23 weeks: 10-35% survival rate
- 24 weeks: 40-70% survival rate
- 25 weeks: 50-80% survival rate
- 26 weeks: 80-90% survival rate
- 27 weeks: greater than 90% survival rate
Physicians cannot predict long-term complications of prematurity and some consequences may not become evident until the child is school--aged. 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, weight at birth, and the presence or absence of breathing problems. The development of infection or the presence of a birth defect can also effect long term prognosis. Severe disabilities like brain damage, blindness, and chronic lung problems are possible and may require ongoing care.
Some of the risks and complications of premature delivery can be reduced if the mother receives good prenatal care, follows a healthy diet, avoids alcohol consumption, and refrains from cigarette smoking. In some cases of premature labor, the mother may be placed on bed rest or given drugs that can stop labor contractions for days or weeks, giving the developing infant more time to develop before delivery. The physician may prescribe a steroid medication to be given to the mother before the delivery to help speed up the baby's lung development. The availability of neonatal intensive care unit, a special hospital unit equipped and trained to deal with premature infants, can also increase the chances of survival.
- A long pause in breathing.
- Dubowitz exam
- Standardized test that scores responses to 33 specific neurological stimuli to estimate an infants neural development and, hence, gestational age.
- Intraventricular hemorrhage (IVH)
- A condition in which blood vessels within the brain burst and bleed into the hollow chambers (ventricles) normally reserved for cerebrospinal fluid and into the tissue surrounding them.
- Yellow discoloration of skin and whites of the eyes that results form excess bilirubin in the body's system.
- Necrotizing enterocolitis (NEC)
- A condition in which part of the intestines are destroyed as a result of bacterial infection.
- Respiratory distress syndrome (RDS)
- Condition in which a premature infant with immature lungs does not develop surfacant, a protective film that helps air sacs in the lungs to stay open. The most common problem seen in premature infants.
- Retinopathy of prematurity
- A condition in which the blood vessels in a premature's infant's eyes do not develop normally, and can, in some cases, result in blindness.
- A protective film that helps air sacs in the lungs to stay open. Premature infants may not have developed this protective layer before birth and are more susceptible to respiratory problems without it. Some surfactant drugs are available. These can be given through a respirator and will coat the lungs when the baby breaths the drug in.
For Your Information
- O'Shea, T. Michael, et al. "Survival and Developmental Disability in Infants with Birth Weights of 501 to 800 grams, Born between 1979 and 1994." Pediatrics 100 (December 1997): 982-986.
- Trachtenbarg, D. E. and T. C. Miller. "Office Care of the Small, Premature Infant." Primary Care 22 (March 1995): 1-21.
- Brazy, J. E. For Parents of Preemies. http://www2.medsch.wisc/childrenshosp/parents_of_preemies/.
- Levison, Donna. "When Is It Too Early? A Guide to Help Prevent Premature Birth." Health Net. http://www.health-net.com/preme.htm.
- "Survival of Extremely Premature Babies." Dr. Plain Talk Health Care Information. http://www.drplaintalk.org.
Gale Encyclopedia of Medicine. Gale Research, 1999.