Gestational age is determined by an assessment of various physical signs (Fig. 58-3) and neuromuscular characteristics (Fig. 58-4) that vary according to fetal age and maturity. Physical criteria mature with advancing fetal age, including increasing firmness of the pinna of the ear; increasing size of the breast tissue; decreasing fine, immature lanugo hair over the back; and decreasing opacity of the skin. Neurologic criteria mature with gestational age, including increasing flexion of the legs, hips, and arms; increasing tone of the flexor muscles of the neck; and decreasing laxity of the joints. These signs are determined during the first day of life and are assigned scores. The cumulative score is correlated with a gestational age, which is usually accurate to within 2 weeks (Fig. 58-5).
Gestational age assessment permits the detection of abnormal fetal growth patterns, aiding in predicting the neonatal complications of largeness or smallness for gestational age (Fig. 58-6). Infants born at a weight greater than the 90th percentile for age are considered large for gestational age. Among therisks associated with being large for gestational age are all the risks of the infant of a diabetic mother and risks associated with postmaturity. Infants born at a weight less than 10th percentile for age (some growth curves use <2 standard deviations or the 5th percentile) are small for gestational age and have IUGR. Problems associated with small for gestational age infants include congenital malformations, in addition to the problems listed in Table 58-2.
The skin should be evaluated for pallor, plethora, jaundice, cyanosis, meconium staining, petechiae, ecchymoses, congenital nevi, and neonatal rashes. Vasomotor instability with cutis marmorata, telangiectasia, phlebectasia (intermittent mottling with venous prominence), and acrocyanosis (feet and hands) is normal in a premature infant. Acrocyanosis also may be noted in a healthy term infant in the first days after birth.
The skin is covered with lanugo hair, which disappears by term gestation. Hair tufts over the lumbosacral spine suggest a spinal cord defect. Vernix caseosa, a soft, white, creamy layer covering the skin in preterm infants, disappears by term. Post-term infants often have peeling, parchment-like skin. Mongolian spots are transient, dark blue to black pigmented macules seen over the lower back and buttocks in 90% of African American, Indian, and Asian infants. Nevus simplex (salmon patch), or pink macular hemangioma, is common, usually transient, and noted on the back of the neck, eyelids, and forehead. Nevus flammeus, or port-wine stain, is seen on the face and should cause the examiner to consider Sturge-Weber syndrome (trigeminal angiomatosis, convulsions, and ipsilateral intracranial tram-line calcifications).
Figure 58-4 Neuromuscular criteria for assessment of maturity and gestational age. Expanded New Ballard Score (NBS) includes extremely premature infants and has been refined to improve accuracy in more mature infants. (From Ballard JL, Khoury JC, Wedig K, et al: New Ballard Score, expanded to include extremely premature infants, J Pediatr 119:417-423, 1991.)