Prematurity

by Adam A. Rosenberg, M.D.
Director of Newborn Services at University Hospital
Professor of Pediatrics at the University of Colorado School of Medicine
Denver, Colorado

What is prematurity?

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.

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What is important to know prior to the birth of a premature infant?

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.

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What is the chance of survival for a premature infant?

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.

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What is the delivery room management of the premature infant?

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.

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What problems can be expected in the nursery?

Thermoregulation

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.

Nutrition

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.

Monitoring

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.

Lung problems

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.

Hyperbilirubinemia (jaundice)

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”).

Infection

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.

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What needs to happen for my baby to go home?

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.

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What is the outcome for survivors of the intensive care nursery?

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.

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References

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