A nurse is assessing a postterm newborn who was born at 42 weeks gestation. Which assessment finding would be most characteristic of postterm infants?

Postterm infants have dry, cracked, peeling skin with minimal subcutaneous fat due to prolonged amniotic fluid exposure and placental insufficiency. Other options describe typical findings in preterm or term infants.

Understanding Postterm Newborn Assessment

When a pregnancy extends beyond 42 weeks gestation, the intrauterine environment begins to deteriorate, leading to a characteristic set of physical findings in the newborn. The placenta, which serves as the lifeline for fetal oxygenation and nutrition, undergoes aging and calcification, progressively compromising its function. This pathophysiological process directly shapes the clinical presentation of a postterm infant.

The most characteristic finding is dry, cracked, and peeling skin with minimal subcutaneous fat. Here is why this occurs:

Loss of Protective Barrier
Vernix caseosa, the thick, cheesy protective coating that shields fetal skin from amniotic fluid, begins to diminish and disappear after 40 weeks. Without this barrier, the skin is directly exposed to amniotic fluid for a prolonged period, resulting in a macerated then desiccated appearance. Upon delivery, this manifests as peeling, parchment-like skin.

Depletion of Energy Reserves
The aging placenta becomes less efficient at transferring oxygen and nutrients. In response, the fetus begins to catabolize its own glycogen and subcutaneous fat stores for energy. This leads to the classic wasted appearance of a postterm infant: loose, wrinkled skin with a notable absence of the plump, well-hydrated look seen in term newborns. The loss of subcutaneous tissue is a hallmark of placental insufficiency.

Why the Other Options Are Incorrect

- Option 1 (Abundant vernix caseosa): This is a finding typical of a preterm infant. Vernix production peaks around the third trimester and is abundant in babies born before 38 weeks. A postterm infant will have little to none.
- Option 3 (Fine, downy lanugo hair): Lanugo is the fine hair that covers the fetal body, appearing around 20 weeks and beginning to shed around 36 weeks. A postterm newborn will have very little lanugo remaining, as most has been shed into the amniotic fluid.
- Option 4 (Soft, pliable ear cartilage): Ear cartilage develops and becomes more rigid with increasing gestational age. Soft, easily folded ears are a sign of prematurity. A postterm infant’s ear cartilage is typically firm with a well-defined shape and instant recoil when folded.

Clinical Implications
The assessment of a postterm newborn requires vigilance for complications linked to placental insufficiency, such as meconium aspiration syndrome, hypoglycemia due to depleted glycogen stores, and polycythemia from chronic intrauterine hypoxia. The physical findings of a wrinkled, peeling appearance with reduced subcutaneous tissue are the direct visual cues that alert the nurse to these underlying risks.