A preterm birth refers to any baby born before the thirty-seventh week of pregnancy. Infants born prematurely can be further classified into three categories based on birth weight. Low-birth-weight (LBW) infants are those with a birth weight below 2500 grams. A very low-birth-weight (VLBW) infant weighs less than 1500 grams, and an extremely low-birth-weight (ELBW) infant weighs less than 1000 grams. Although an infant born at 25 weeks’ and one born at 35 weeks’ gestation are both considered premature, the medical concerns and care required to support each differ considerably in terms of required resources, and the infants may have vastly different outcomes.

Major concerns relating to prematurity include stabilization in the delivery room and evaluation of the degree of immaturity of vital organ systems. Following initial stabilization, attention is closely paid to ongoing cardiorespiratory needs, hemodynamic status, fluid administration, electrolyte monitoring, neurologic status, temperature stability, likely infectious complications, and ultimately feeding tolerance and readiness for discharge. It is these factors that will ultimately determine the duration of the infant’s neonatal intensive care unit (NICU) stay. A systems approach is best in identifying and providing overall medical needs of the infant:

Cardiovascular: Hemodynamic stability is an important consideration requiring ongoing monitoring, with indwelling catheters required in the smallest and sickest of patients. Fluctuations in blood pressure may affect the pressure passive cerebral circulation. The effect of a large patent ductus arteriosus may impact the respiratory, cardiac, and renal systems and pose a risk to blood supply to the gastrointestinal (GI) tract.

Infectious Disease: Perinatal and postnatal infection, in the face of an immature immune system, can pose a tremendous challenge, affecting the infant’s respiratory status, hemodynamic stability, fluid and electrolyte balance, and ultimate neurodevelopmental outcome.

Neurologic: Early serial evaluations for intraventricular/intracranial hemorrhage and periventricular leukomalacia play a vital role in counseling families about possible long-term neurodevelopmental concerns, but extreme caution must be maintained in making predictions of long-term neurodevelopmental outcome based on ultrasound findings.

Developmental immaturity of the respiratory control centers can result in apnea of prematurity. For some preterm infants the resultant apnea, bradycardia, and desaturation events may be few and self-limiting; however, for others, these events can be quite frequent, requiring significant stimulation. Medical therapy with caffeine has been used. Intubation is occasionally necessary.

Pulmonary: Respiratory distress syndrome (RDS) (see Chapter 73, Respiratory Distress Syndrome), resulting from an immaturity in lung surfactant development, carries a risk for development of air leaks, including pneumothorax and pulmonary interstitial emphysema. The respiratory system is often the focus of care during the initial hours, days, and possibly weeks of a premature infant’s life. The most preterm infants, those less than 26 completed weeks’ gestation, are most susceptible to respiratory complications as a result of both an immature pulmonary surfactant system and also an arrest of alveolar development. Most infants below 28 weeks’ gestation will require intubation and mechanical ventilation with surfactant administration and supplemental oxygen as needed to adequately support oxygenation. Efforts are made to avoid hyperoxia in preterm infants under 32 to 34 weeks due to concerns of free radical production and its impact on lung tissue injury as well as on the developing retinal vasculature, leading to retinopathy of prematurity (ROP). Many NICUs have adopted target oxygen saturation levels that range from 88% to 92% for infants on increased ambient oxygen as an effort to prevent the deleterious effects of hyperoxia.

Gastrointestinal: Intravenous access via either an umbilical catheter or peripheral intravenous line is needed to ensure adequate fluid administration, caloric intake, and hemodynamic stability. A central venous catheter (i.e., percutaneous central venous line (PCVL), peripherally inserted central catheter [PICC]) may be required to ensure maximal caloric intake that favors optimal growth. When on sufficient parenteral caloric support, fluid requirements of 120 to 140 mL/kg/day can provide sufficient caloric support of 120 kcal/kg/day for a growing preterm infant. Infants under 750 g may require even higher fluid amounts as a result of significant insensible fluid losses through their immature skin. Because urine output is not a reliable marker of fluid status in the first 24 to 48 hours of life, monitoring serum electrolytes at a regular interval will assist in assessing overall fluid status. Frequent blood monitoring carries the high likelihood of need for blood transfusion, and efforts should be made to minimize exposure to multiple donors.

Early initiation of enteral nutrition, otherwise called “trophic feeds” of volume ≤10 mL/kg/day, via a nasogastric or orogastric tube in hemodynamically stable preterm infants is encouraged. Trophic feedings aid in priming the immature gut, encourage normal gastrointestinal hormonal release, and have not been associated with increased incidence of necrotizing enterocolitis, which is a significant pathologic condition in preterm infants (see Chapter 72, Necrotizing Enterocolitis).

All mothers of preterm infants should be encouraged to provide breast milk feedings for their infants because the immunologic benefits of breast milk have yet to be matched by specially designed preterm infant formulas. Once feeds are tolerated, they can be advanced by ≤20mL/kg/day. Fortification of breast milk is usually necessary to provide the appropriate caloric intake as well as calcium and phosphorus requirements for a growing preterm infant. As the preterm infant approaches 33 to 34 weeks and demonstrates a coordinated suck-swallow-breathing mechanism, the advancement to oral bottle feeding or breastfeeding may begin.

Ophthalmologic: Retinopathy of prematurity (ROP) screening protocols exist in most NICUs to follow retinal vascular development and identify those at high risk for ROP requiring intervention with laser therapy. Current standards are to screen all infants under 1500 g or less than 28 weeks or those with an unstable clinical course felt to be at high risk by the attending caregiver.