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Late Preterm Infant

By Eric Gibson, MD, Associate Professor, Neonatal-Perinatal Medicine;Attending Physician, Sidney Kimmel Medical College of Thomas Jefferson University;Nemours/A.I. duPont Hospital for Children ; Ursula Nawab, MD, Associate Medical Director, Newborn/Infant Intensive Care Unit and Attending Neonatologist, Division of Neonatology, Children’s Hospital of Philadelphia

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Patient Education

A late preterm infant is an infant born ≥ 34 wk and < 37 wk gestation.

Full-term gestation is 40 wk (range 37 to 42 wk). Late preterm infants often appear to be the size of full-term infants but have increased morbidity due to their prematurity. Late preterm births represent nearly three quarters of all preterm births. The rate of late preterm birth has increased in the past 2 decades from 7.2% in 1990 to 8.3% in 2011; many late preterm deliveries are medically indicated.


Late preterm delivery is sometimes medically indicated (eg, because of preeclampsia, placenta previa/placenta accreta, or premature rupture of membranes) and is often done using cesarean delivery.

In a given patient, the cause of spontaneous late preterm labor and delivery is usually unknown. However, risk factors are similar to those of preterm birth in general (see Premature Infant : Etiology) and chronic chorioamnionitis may be associated with spontaneous late preterm deliveries.


Although clinicians tend to focus on the more dramatic and obvious complications of premature infants born < 34 wk gestation, late preterm infants are at risk of many of the same disorders. They have longer hospital stays and higher incidence of readmission and diagnosed medical disorders than term infants. Most complications relate to dysfunction of immature organ systems and are similar to, but typically less severe than, those of infants born more prematurely (see Premature Infant : Complications). However, some complications of prematurity (eg, necrotizing enterocolitis, retinopathy of prematurity, bronchopulmonary dysplasia, intraventricular hemorrhage) are rare in late preterm infants. In most cases, complications resolve completely.

Complications include the following:

  • CNS: Apneic episodes (see Apnea of Prematurity)

  • GI tract: Poor feeding due to delayed maturation of the suck and swallow mechanism (primary reason for prolonged hospital stay and/or readmission)

  • Hyperbilirubinemia: Caused by immature mechanisms for hepatic bilirubin metabolism and/or increased intestinal reabsorption of bilirubin (eg, if feeding difficulties cause decreased intestinal motility—see Neonatal Hyperbilirubinemia)

  • Hypoglycemia: Caused by low glycogen stores (see Neonatal Hypoglycemia)

  • Lungs: Respiratory distress syndrome (caused by inadequate surfactant production—see Respiratory Distress Syndrome in Neonates); transient tachypnea of the newborn (see Transient Tachypnea of the Newborn)

  • Temperature instability: Some degree of hypothermia in half of infants (caused by increased surface area to volume ratio, decreased adipose tissue, and ineffective thermogenesis from brown fat—see Hypothermia in Neonates)


  • Gestational age estimated by new Ballard score

  • Routine screening for metabolic complications

Findings on physical examination correlate with gestational age (see Figure: Assessment of gestational age—new Ballard score.).

Glucose monitoring is necessary for at least 24 h, particularly if regular feedings have not been well established. Routine evaluations include pulse oximetry, serum Ca and electrolytes, CBC, and bilirubin level.

Infants must be monitored for apnea and bradycardia until they are 34.5 to 35 wk adjusted age or until event free. Glucose levels are monitored for at least 24 h, particularly if regular feedings have not been well established. Bilirubin levels are monitored clinically in the first week of life.


Prognosis varies with presence and severity of complications, but usually mortality and likelihood of complications decrease greatly with increasing gestational age and birth weight.

Most CNS problems resolve. Breathing control is usually mature by 37 to 38 wk gestation, and apneic events cease by 43 wk. However, some children have mild delays in development and school-related problems, so all should have neurodevelopmental follow-up and appropriate early referral to intervention programs as needed.

Lung problems usually resolve, but some infants develop pulmonary hypertension.


  • Supportive care

Identified disorders are treated. For infants without specific conditions, support focuses on body temperature and feeding.

Preterm infants can be stressed by the metabolic demands of maintaining core body temperature (see Hypothermia in Neonates). Thus, they should be kept in a neutral thermal environment, which is the environmental temperature at which metabolic demands (and thus calorie expenditure) to maintain body temperature in the normal range are lowest. The neutral thermal environment has a narrow range from 36.7° C to 37.3° C.

Breastfeeding is strongly encouraged. Most late preterm infants tolerate breast milk, which provides immunologic and nutritional factors that are absent in cow’s milk formulas. If infants do not suck and/or swallow adequately, feedings should be given by NGT beginning with small amounts and gradually increasing over time.

Key Points

  • Although late preterm infants (≥ 34 wk and < 37 wk gestation) may appear to be similar in size and appearance to term infants, they are at increased risk of complications.

  • Complications include hypothermia, hypoglycemia, respiratory distress syndrome, hyperbilirubinemia, and poor feeding.

  • Treat disorders and support body temperature and feeding.

  • Provide neurodevelopmental follow up to identify and address any disabilities.