Any infant born at less than 37 weeks gestation is by definition "premature." Most infants born at 35 to 37 weeks gestation are relatively healthy, and they often have only brief hospital stays in normal newborn nurseries. The problems associated with premature infants occur with greater frequency in those of lower gestational age at birth, typically less than 35 weeks gestation.
Some treatments may be used in mothers who are at risk of having their baby early. Anyone who has had a previous preterm infant is at a "high risk" of having another preterm infant. Therefore, prenatal care should be sought with a caregiver who is up to date and comfortable with the management of a mother who is at risk for a preterm delivery.
When a mother is in preterm labor, she should be admitted to the hospital and placed on drugs to slow the progress of labor. Although these drugs will not delay delivery for very long in many cases, they often allow enough time to receive a full course of steroids (betamethasone or dexamethasone) to accelerate the maturation of the fetus. Steroids have been shown to decrease the rate of death of preterm infants, as well as decrease the rate of lung, intestinal, and brain complications.
When there is a risk of delivering a baby early, it is appropriate to ask if the nursery at the hospital is able to take care of a preterm baby. If not-if it is safe for the mother and fetus-they should be transferred to a facility that is capable of caring for the baby after birth. In addition, an expectant mother should talk with the hospital staff members who will care for the baby after birth. Issues to discuss include a review of the problems associated with prematurity, chances of survival, and the anticipated long-term outcome.
The survival of premature infants is determined by gestational age at delivery and birth weight. Infants born after 28 weeks gestation and 1,000 grams, or 3 pounds 3 ounces (454 grams equals 1 pound), have more than a 90% chance of survival. The rate of survival at 27 weeks and 900 grams is 80% to 85%, at 26 weeks and 800 grams is 75% to 80%, and at 25 weeks and 700 grams is 60%. Rates of survival drop off rapidly at less than 25 weeks, and they vary quite a bit among different nurseries.
The long-term outcome also is dependent on gestational age and birth weight. For babies of 26 to 32 weeks gestation, the rate of severe neurodevelopmental problems among survivors is about 10%; at 23 to 26 weeks, the rate increases gradually to 25% of survivors. Other long-term complications, including lung problems, vision disturbances, and hearing loss, are more common in babies of lower gestational age at birth.
Staff members who are experienced in the management of premature infants should be present in the delivery room. The infant must be kept warm; provided with adequate oxygen; and helped with breathing, if necessary. Most infants who weigh less than 1,000 grams at birth will require a breathing tube in their airway.
Preterm infants are not able to maintain their body temperature without an external heat source. Initially, heat will be provided with an overhead warmer that responds to the baby's temperature and provides adequate warmth to maintain a normal body temperature. The warmer provides easy access to the baby for necessary cares during the early, "unstable" period. When more stable, the baby will be moved into an incubator to maintain a warm environment. Most infants are able to move into an open crib at a weight of approximately 1,800 grams.
Initially, premature infants are given all the necessary fluid, calories, protein, sugar, and fat in their veins. When their condition stabilizes, a feeding tube into their stomachs can start. The amount of feeds starts at a very low level, and it is advanced slowly over 3 to 7 days to "full" feeds. At this point, the infant no longer needs fluids or nutrition into their veins. Once full feeds are achieved, anticipated rates of weight gain are 10 to 25 grams per day. Breast milk is the food of choice, but formulas developed for preterm infants are an acceptable substitute. A baby will be able to begin "nipple" feeding from a bottle at about 33 to 34 weeks post conception.
All babies in intensive care nurseries have their heart rates, breathing, and, in some cases, blood pressure monitored continuously. Blood oxygen also can be monitored with a pulse oximeter in infants with lung and heart problems. A pulse oximeter uses a light source, wrapped around the infant's foot or hand, to measure the amount of oxygen carried by the hemoglobin in the red blood cells. At the start, a sick baby will usually have an indwelling tube in an artery (usually the umbilical artery in the cord that was connected to the placenta in the uterus) to sample blood for tests without having to draw blood from the infant. A tube also may be placed in the umbilical vein to give fluids and nutrition. These tubes are usually kept in the infant for 3 to 10 days depending on how sick they are.
Hyaline membrane disease (HMD) or respiratory distress syndrome (RDS). By 24 weeks gestation, there is adequate surface for gas exchange (bringing oxygen to the blood and removing carbon dioxide) in the lung; however, a necessary element for survival is missing. The natural tendency of a lung is to collapse when a person breathes out. Once collapsed, it is very difficult to reopen the lung. A chemical called surfactant is produced in the lungs to lower surface tension as the lungs get smaller during exhalation. This chemical prevents a total collapse of the lungs and allows easy re-expansion with inhalation.
Preterm babies have little or no surfactant in their lungs, and they would die from respiratory failure without intervention. The frequency of surfactant deficiency ranges from nearly 100% at 24 weeks gestation, to 60% at 28 weeks and 25% at 32 weeks. To treat this condition, babies are given surfactant substitutes through their breathing tubes into the lungs and to help them breathe with breathing machines called ventilators. Depending on their gestation at birth, premature infants will remain on the ventilator from a few days to up to about 6 weeks.
When babies are ready to come off the ventilator, they are "extubated" (removal of the breathing tube) to either nasal CPAP (provides low pressure through a device placed in the nose to help keep the lungs expanded) or to a bubble with extra oxygen placed over the head. Ultimately, supplemental oxygen can be delivered with a small hose under the nose called a nasal cannula.
Apnea and bradycardia (A&B spells). At the time of birth, preterm infants have an immature respiratory drive. This results in spells when they "forget" to breathe (apnea). If these spells are long enough, they result in a decrease in blood oxygen and then a slowing of the heart rate (bradycardia). Sometimes, these episodes resolve themselves, while, in other cases, the infants need to be stimulated to restart breathing. If the spells are bad enough or occur with a frequency of more than 6 to 10 times per day, they can be treated medically with caffeine (like in coffee) citrate.
In most infants, this is successful; however, if this treatment fails, it is sometimes necessary to place the infant back on nasal CPAP or the ventilator. Infants born beyond 28 weeks gestation generally outgrow these spells by 37 weeks post conception. In infants born at lower gestational ages, the spells may last longer.
Chronic lung disease (CLD) or bronchopulmonary dysplasia (BPD). The combination of prematurity, oxygen exposure, and mechanical ventilation can result in lung injury to preterm babies. The consequence of this lung injury is chronic lung disease. CLD can prolong ventilator courses in small preterm infants (less than 1,200 grams) and result in a long-term oxygen need that can sometimes extend to home care. The frequency of this complication is greatest in the least mature infants, and, in those infants less than 26 weeks gestation at birth, it can occur in over 75% of cases. However, the lungs still generate new gas exchange surface until adolescence so the vast majority of infants outgrow this problem.
Patent ductus arteriosus (PDA)
The major heart-related problem in premature infants is PDA. The ductus is a structure that is present in a fetus connecting the main blood vessel that goes to the lungs from the heart to the main blood vessel that goes to the rest of the body. In the fetus, very little blood goes to the lungs because the fetus does not breathe air. The ductus allows the majority of the blood that is headed from the heart to the lungs to cross to the circulation to the body, bypassing the lungs. At birth, it is supposed to close.
In preterm babies, this closure may not occur. After birth, if this vessel is open, too much blood ends up going to the lungs, making it harder for an infant to breathe or to be ventilated. To close this blood vessel, the medication indomethacin is used. This works over 75% of the time; however, if it fails, a surgical closure is needed. Fortunately, it is a brief procedure that can be done at the bedside with almost uniformly good results.
Necrotizing enterocolitis (NEC)
The most important intestinal complication in preterm babies is NEC. This disease is the result of periods of low blood flow to the intestine, intestinal immaturity, and infection. When a baby develops this problem, they cannot be fed into the intestine and require 10 to 21 days of nutrition in their veins. In addition, a large tube is placed in the stomach to keep air out, and antibiotics are given. Many of the cases respond to this treatment, but, in some cases, surgery is needed to remove parts of the intestine that have died.
Intraventricular hemorrhage (IVH)
The internal structures of the brain in a preterm infant are at risk for hemorrhage. The bleeding is usually the result of a previous period of low blood flow, and occurs in the first four days of life. Diagnosis of the bleeding is performed with bedside ultrasound exams. The degree of bleeding is graded from 1 to 4. Grade 1 and 2 bleeds are small, and they do not increase the infant's risk of neurodevelopmental abnormalities, while 33% of the babies with grade 3 and 4 bleeds will suffer severe neurologic injury, and another 33% will suffer lesser deficits. The final neurologic complication in preterm babies is injury to the motor tracts in the brain called periventricular leukomalacia (PVL), which causes cerebral palsy-a movement disorder with spasms that can impair the ability to walk.
Retinopathy of prematurity
The retina of the preterm infant is not fully "vascularized"(i.e., the blood vessels are not fully developed) at birth. The infant is at risk for a process called ROP, which, in its worst form, can lead to detachment of the retina and blindness. In babies born at less than 28 weeks or 1,500 grams, an ophthalmologist will perform a screening exam at 6 weeks of age.
Follow-up exams will then be performed until any ROP resolves, and the retina is fully vascularized. ROP is graded from 1 to 5 for severity. The process resolves spontaneously in most infants, but those infants who reach an advanced stage 3 of disease are at a high risk for detachment of the retina. These infants require treatment with laser therapy, which often can save the vision in the affected eye(s).
Anemia of prematurity
Because of blood sampling for tests and conditions that cause blood loss, such as inventricular hemorrhage, many preterm babies will require red blood cell transfusions. To decrease the number of transfusions given and to minimize donor exposure, preterm babies can be treated with the hormone erythropoietin, which stimulates red blood cell production in the body.
Virtually all preterm babies will develop jaundice. Jaundice is caused by an accumulation of the yellow pigment "bilirubin," which is the breakdown product of hemoglobin from the red blood cells. A preterm infant cannot effectively clear the bilirubin in the liver. If too much bilirubin accumulates in the blood, it can cause brain damage. To help these infants in clearing the bilirubin to prevent brain damage, they are placed under phototherapy ("bilirubin lights").
Some preterm deliveries are the result of an infection in the uterus, which also can lead to an infection in the baby. In addition, infants in the intensive care nursery are at an increased risk for infection due to indwelling lines and tubes, as well as a compromised immune ("infection fighting") system. Thus, the risk of infection is high. If there is concern that an infant might be infected or there is a proven infection, the infant is treated with antibiotics-an event that is likely to occur more than once during the nursery stay.
Most preterm infants are ready for discharge at or a few weeks before their due date. The criteria for discharge include the ability to maintain body temperature in a crib, adequate oral intake to sustain consistent growth, and resolution of apneic and bradycardic spells. Occasionally, infants who are otherwise doing well may be sent home on partial tube feedings.
In addition, if A&B spells are not completely resolved, but are not felt to be life threatening, some physicians will send a baby home on a heart monitor. If an infant needs supplemental oxygen at discharge, a test needs to be performed prior to going home to be sure if the oxygen were to fall off that the blood oxygen does not drop to dangerously low levels.
Neurodevelopmental handicaps may occur in survivors of the intensive care nursery. These handicaps include cerebral palsy, which can be severe enough to prevent a child from walking, and cognitive deficits, which can be severe enough to prevent a child from learning to talk or read. Fortunately, deficits this severe occur in the minority of survivors, but others may have lesser deficits that cause delayed motor development, learning disabilities, and behavioral disorders, such as attention deficit disorder (hyperactivity).
The rates of abnormalities are higher in babies of lower gestational age at birth, particularly those born at 25 weeks or less. Although ROP rarely causes blindness, vision problems may still occur. The frequency of hearing loss is increased compared to term infants. The consequences of chronic lung disease are an increased rate of hospital readmission during the first two years of life, a continued oxygen need, and an increased incidence of asthma-like symptoms.
Finally, preterm infants are at an increased risk for poor weight gain, and they may require nutritional supplements or special formulas. Most premature infants who "graduate" from an intensive care nursery do quite well; however, coordinated follow-up to address all of their needs is of paramount importance.
Fanaroff A.A., Martin R.J. (editors): Neonatal-Perinatal Medicine. Diseases of the Fetus and Infant, 6th ed., Mosby, 1997.
Zaichkin J.: Newborn Intensive Care. What Every Parent Needs to Know. NICU Ink, 1996.
About the Author
Dr. Rosenberg graduated from Vanderbilt Medical School in 1976. His Pediatric Residency was at the University of Colorado and his Neonatal Fellowship was fulfilled at Johns Hopkins University. He is the Director of Newborn Services at University Hospital in Denver and Professor of Pediatrics at the University of Colorado School of Medicine.
His professional interests include newborn brain injury and long-term follow up of high-risk newborns. Some of his personal interests include tennis, skiing and youth sports programs.
Copyright 2012 Adam A. Rosenberg, M.D., All Rights Reserved