Merck Manual

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Postterm Infants


Arcangela Lattari Balest

, MD, University of Pittsburgh, School of Medicine

Reviewed/Revised Nov 2023

A postterm infant is an infant born at ≥ 42 weeks of gestation.

Pathophysiology of Postterm Infants

In most cases, fetal growth continues until delivery. However, in some cases, the placenta involutes as pregnancy progresses and multiple infarcts and villous degeneration develop, causing placental insufficiency. In these cases, the fetus receives inadequate nutrients and oxygen from the mother, resulting in a thin (due to soft-tissue wasting), undernourished infant with depleted glycogen stores and decreased amniotic fluid volume. Such infants are dysmature and, depending on when placental insufficiency develops and the severity of the condition, they may be small-for-gestational-age Small-for-Gestational-Age (SGA) Infant Infants whose weight is < the 10th percentile for gestational age are classified as small for gestational age. Complications include perinatal asphyxia, meconium aspiration, polycythemia... read more . Although placental insufficiency with dysmaturity can occur at any gestational age, it is most common in pregnancies that progress beyond 41 to 42 weeks.


Postterm infants have higher morbidity and mortality than term infants due in large part to

  • Perinatal asphyxia

  • Meconium aspiration syndrome

  • Neonatal hypoglycemia

Perinatal asphyxia may result from placental insufficiency as well as cord compression secondary to oligohydramnios.

Neonatal hypoglycemia Neonatal Hypoglycemia Hypoglycemia is difficult to define in neonates but is generally considered a serum glucose concentration < 40 mg/dL (< 2.2 mmol/L) in symptomatic term neonates, < 45 mg/dL (< 2... read more is a complication caused by insufficient glycogen stores or by increased production of insulin (most commonly caused by maternal diabetes) in the fetus. Because anaerobic metabolism rapidly uses the remaining glycogen stores, hypoglycemia is exaggerated if perinatal asphyxia has occurred.

Symptoms and Signs of Postterm Infants

Postterm infants are alert and appear mature. They have a decreased amount of soft-tissue mass, particularly subcutaneous fat. The skin may hang loosely on the extremities and is often dry and peeling. The fingernails and toenails are long. The nails, skin, and umbilical cord may be stained with meconium passed in utero.

Diagnosis of Postterm Infants

  • Gestational age and physical examination

  • Early term: 37 to 38 6/7 weeks

  • Full term: 39 to 40 6/7 weeks

  • Late term: 41 to 41 6/7 weeks

  • Postterm: ≥ 42 weeks

Diagnosis reference

Treatment of Postterm Infants

  • Treatment of complications

Improved obstetric care over the past 2 decades has markedly decreased the number of infants delivered past 41 weeks of gestation, which has also decreased the incidence of meconium aspiration syndrome.

Postterm and dysmature infants are at risk of hypoglycemia and should be monitored and managed accordingly.

For infants with perinatal asphyxia, management depends on the severity of the disease process. Therapeutic hypothermia may help infants with moderate or severe encephalopathy who had severe acidosis at birth, a low Apgar score at ≥ 5 minutes, and/or a need for prolonged resuscitation.

Neither the incidence nor the severity of meconium aspiration syndrome Meconium Aspiration Syndrome Intrapartum meconium aspiration can cause inflammatory pneumonitis and mechanical bronchial obstruction, causing a syndrome of respiratory distress. Findings include tachypnea, rales and rhonchi... read more is reduced by endotracheal suction at the time of delivery, regardless of the apparent viscosity of the fluid or the infant's level of activity, so endotracheal intubation should be reserved for infants who need ventilatory assistance or who seem to have obstruction of the airway caused by meconium. Infants with meconium aspiration syndrome may require assisted ventilation; high-frequency ventilation Mechanical Ventilation Initial stabilization maneuvers include mild tactile stimulation, head positioning, and suctioning of the mouth and nose followed as needed by Supplemental oxygen Continuous positive airway... read more is sometimes helpful. Sedation is often necessary.

Surfactant treatment does not decrease overall mortality but does reduce the likelihood of the need for treatment with extracorporeal membrane oxygenation Extracorporeal Membrane Oxygenation (ECMO) Initial stabilization maneuvers include mild tactile stimulation, head positioning, and suctioning of the mouth and nose followed as needed by Supplemental oxygen Continuous positive airway... read more (ECMO), so surfactant is frequently used in infants with significant respiratory distress. ECMO is available in a relatively few neonatal centers and generally is reserved for infants ≥ 34 weeks of gestation with hypoxic respiratory failure refractory to conventional medical treatment.

NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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