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Postmature Newborn

By Robert L. Stavis, PhD, MD, Clinical Director, Neonatal ICUs; Associate Professor, Department of Pediatrics, Main Line Health, Bryn Mawr, PA; Department of Pediatrics, Nemours/Alfred I. duPont Hospital for Children; Thomas Jefferson University Hospital

A postmature newborn is a baby delivered after gestational age of 42 weeks or more.

  • 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 postmature newborns.

  • Postmature 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 date of delivery.

  • Typically treatment focuses on providing good nutrition and general care.

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

Gestational age refers to how far along the pregnancy is. The gestational age is the number of weeks that have passed since the first day of the mother's last menstrual period. 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

  • Premature: Delivered before 34 weeks of gestation.

  • Late preterm: Delivered at 34 to before 37 weeks of gestation.

  • Full term: Delivered at 37 to before 41 weeks of gestation.

  • Late term: Delivered at 41 to before 42 weeks of gestation.

  • Postmature: Delivered at 42 weeks or more of gestation.

Postmature (postterm) delivery is much less common than premature (preterm) delivery. Why a pregnancy continues beyond term is usually unknown. Women 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. 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, postmature newborns are prone to developing low blood sugar (glucose) levels (hypoglycemia) because they have exhausted their supply of stored fat and carbohydrates.

Symptoms

Postmature newborns 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 and nails may be stained green if meconium was present in the amniotic fluid.

Diagnosis

  • Appearance of the newborn

  • Estimated due date

Doctors base the diagnosis of postmaturity on the newborn's appearance after birth and on the calculated gestational age.

Treatment

  • 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, and decrease the possibility that the baby will have meconium aspiration syndrome. Postmature newborns who have low oxygen levels and fetal distress may need to be urgently delivered by cesarean delivery and may need to be revived (resuscitated) at birth.

If the baby has breathed meconium into the lungs, 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 postmature newborns can catch up to the weight that is appropriate for them.