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 gestationare 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. Thesepremature infants, however, are at higher risk for death or serious complications, which include heart defects, respiratory problems, blindness, and brain damage.
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 prematurebirth, 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, andmost important, identifiable cause of prematurity is drug abuse, particularly cocaine, by the mother.
Infants born prematurely may experience major complications due to their lowbirth weight and the immaturity of their body systems. Some of the common problems among premature infants are jaundice (yellow discoloration of the skinand whites of the eyes), apnea (a long pause in breathing), and inability tobreast 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 inpremature 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 cagepull inward with each breath. Sometimes the infant needs extra oxygen, and sometimes a surfactant drug can be given to coat the lung tissue. Bronchopulmonary dysplasia is the development of scar tissue in the lungs, and can occurin severe cases of RDS.
Necrotizing enterocolitis (NEC) is a further complication of prematurity. Inthis 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 forthe 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 includetaking 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 thebrain burst and bleed into the hollow chambers (ventricles) normally reserved for cerebrospinal fluid and into the tissue surrounding them. 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 andinto 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 areimplemented 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 orpurplish hue. Apnea occurs most commonly when the infant is asleep. Infantswith 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 getsolder, and the lungs and brain tissues mature, the breathing usually becomesmore 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 afterbirth. If it does not close, the baby may have trouble getting enough oxygenon 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. Insome cases, a drug, indomethacin, can be given to close the duct. Surgery may be required, or 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 because they are born with fewer antibodies.
Many of the problems associated with prematurity depend on how early the babyis 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 dateof conception or using ultrasound imaging to observe development. Whena 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 tapedon 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 orventilator 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 beadministered 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 orto 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 tobreath and eat unassisted.
Advances in medical care have made it possible for many premature infants tosurvive and develop normally. However, whether or not a premature infant willsurvive is still intimately tied to his or her gestational age. The longer the baby was able to develop in the womb the more likely it will be to surviveoutside it.
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 presenceor absence of breathing problems. The development of infection or the presence of a birth defect can also effect long term prognosis. Severe disabilitieslike brain damage, blindness, and chronic lung problems are possible and mayrequire 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 alcoholconsumption, and refrains from cigarette smoking. In some cases of prematurelabor, 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 todevelop before delivery. The physician may prescribe a steroid medication tobe given to the mother before the delivery to help speed up the baby's lung development. The availability of a neonatal intensive care unit, a special hospital unit equipped and trained to deal with premature infants, can also increase the chances of survival.