Postterm Newborns

ByArcangela Lattari Balest, MD, University of Pittsburgh, School of Medicine
Reviewed/Revised Jan 2024

A postterm newborn is a baby delivered at or after 42 weeks of gestation.

  • Near the end of a term pregnancy, the function of the placenta decreases, providing fewer nutrients and less oxygen to the fetus.

  • Low blood sugar (glucose) is a particular problem in postterm newborns.

  • Postterm newborns have dry, peeling, loose skin and may appear abnormally thin because they have not received sufficient nutrition at the end of the pregnancy.

  • The diagnosis is based on the appearance of the newborn and the estimated gestational age.

  • Typically treatment is focused on providing good nutrition and general care.

  • Some postterm newborns are not breathing at birth and need to be revived (resuscitated).

(See also Overview of General Problems in Newborns.)

Gestational age refers to the number of weeks of pregnancy. The gestational age is determined by counting the number of weeks between the first day of the mother's last menstrual period and the day of delivery. This time frame is often adjusted according to other information doctors receive, including the results of early ultrasound scans, which give additional information regarding the gestational age. The baby is estimated to be due (the due date) at 40 weeks of gestation.

Newborns are classified by gestational age as

  • Preterm: Delivered before 37 weeks of gestation

  • Full term: Delivered at 37 to before 42 weeks of gestation

  • Postterm: Delivered at 42 weeks or more of gestation

Postterm delivery is much less common than preterm (premature) delivery. Why a pregnancy continues beyond term is usually unknown. Pregnant people who have had one postterm delivery are at increased risk of having another one.

Near the end of a term pregnancy, the level of amniotic fluid decreases and the placenta (the organ that provides nourishment to the fetus) becomes smaller and less effective in providing oxygen and nutrients. To compensate, the fetus begins to use its own fat and carbohydrates (sugars) to provide energy. As a result, its growth rate slows, and its weight may even decrease.

Complications during and after delivery

If the placenta shrinks enough, it may not provide adequate oxygen to the fetus, particularly during labor (see Birth Asphyxia). A lack of adequate oxygen may result in fetal distress (signs that the fetus is not well) and, in extreme cases, may result in injury to the brain and other organs.

Fetal distress can cause the fetus to pass meconium (the fetus' stools) into the amniotic fluid. The fetus may reflexively take deep, gasping breaths triggered by the distress and thereby inhale the meconium-containing amniotic fluid into the lungs before birth. As a result, the newborn may have difficulty breathing after delivery (meconium aspiration syndrome).

If the pregnancy continues significantly beyond term, the fetus may die.

After delivery, postterm newborns are prone to developing low blood sugar (glucose) levels (hypoglycemia) because they have exhausted their supply of stored fat and carbohydrates or because they have a high level of insulin. If the fetus has been exposed to high glucose levels because the mother's diabetes was poorly controlled during pregnancy, the fetus usually has a high level of insulin. At the time of delivery, the placental supply of glucose is abruptly stopped, and the high level of insulin can rapidly drop the baby's blood sugar level, resulting in hypoglycemia.

Symptoms of Postterm Newborns

Postterm newborns often have dry, peeling, loose skin and may appear abnormally thin (emaciated), especially if the function of the placenta was severely reduced. The fingernails and toenails are long. The umbilical cord, skin, and nails may be stained green if meconium was present in the amniotic fluid.

Diagnosis of Postterm Newborns

  • Appearance of the newborn

  • Gestational age

The diagnosis of postterm is based on the newborn's appearance after birth and on the calculated gestational age.

Treatment of Postterm Newborns

  • Treatment of complications

If a pregnancy goes beyond term, inducing labor in the mother can decrease the risk of newborn death, decrease the need for cesarean delivery (C-section), and decrease the possibility that the newborn will have meconium aspiration syndrome. Postterm newborns who have low oxygen levels and fetal distress may need to be urgently delivered by C-section and may need to be revived (resuscitated) at birth.

If the baby has breathed meconium into the lungs or is having trouble breathing because of another problem, doctors may give an injection of surfactant (a material that coats the inside of the air sacs and makes it easy to breathe). A machine that helps air get in and out of the lungs (ventilator) and oxygen may be needed to support breathing.

Sugar (glucose) solutions given by vein (intravenously) or frequent breast milk/formula feedings are given to prevent or treat hypoglycemia.

If complications do not occur, the major goal is to provide good nutrition so that postterm newborns can catch up to the weight that is appropriate for them.

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