Two groups of neonates are born weighing less than the normal minimum birth weight of 5½ lb (2,500 g)—those who are born prematurely (before the 37th week of gestation) and those who are small for gestational age (SGA). The premature neonate weighs an appropriate amount for his gestational age and probably would have matured normally if carried to term. Conversely, the SGA neonate weighs less than the normal amount for his age; however, his organs are mature. Differentiating between the two groups, helps direct the search for a cause.
In the premature neonate, low birth weight usually results from a disorder that prevents the uterus from retaining the fetus, interferes with the normal course of pregnancy, causes premature separation of the placenta, or stimulates uterine contractions before term. In the SGA neonate, intrauterine growth may be retarded by a disorder that interferes with placental circulation, fetal development, or maternal health. (See Maternal causes of low birth weight.)
Regardless of the cause, low birth weight is associated with higher neonate morbidity and mortality; in fact, these neonates are 20 times more likely to die within the first month of life. Low birth weight can also signal a life-threatening emergency.
SGA neonates who will demonstrate catch-up growth, do so by 8 to 12 months. Some SGA neonates will remain below the 10th percentile. Weights of the premature neonate should be corrected for gestational age by approximately 24 months.
Because low birth weight may be associated with poorly developed body systems, particularly the respiratory system, your priority is to monitor the neonate’s respiratory status. Be alert for signs of distress, such as apnea, grunting respirations, intercostal or xiphoid retractions, or a respiratory rate exceeding 60 breaths/minute after the first hour of life. If you detect any of these signs, prepare to provide respiratory support. Endotracheal intubation or supplemental oxygen with an oxygen hood may be needed.
Monitor the neonate’s axillary temperature. Decreased fat reserves may keep him from maintaining normal body temperature, and a drop below 97.8° F (36.5° C) exacerbates respiratory distress by increasing oxygen consumption. To maintain normal body temperature, use an overbed warmer or an Isolette. (If these are unavailable, use a wrapped rubber bottle filled with warm water, but be careful to avoid hyperthermia.) Cover neonate’s head to prevent heat loss.
As soon as possible, evaluate the neonate’s neuromuscular and physical maturity to determine gestational age. (See Ballard Scale for calculating gestational age, pages 488 and 489.) Follow with a routine neonatal examination.
This section lists some fetal and placental causes of low birth weight as well as the associated signs and symptoms present in the neonate at birth.
Abnormalities in the number, size, or configuration of chromosomes can cause low birth weight and possibly multiple congenital anomalies in a premature or SGA neonate. For example, a neonate with trisomy 21 (Down syndrome) may be SGA and have prominent epicanthal folds, a flat-bridged nose, a protruding tongue, palmar simian creases, muscular hypotonia, and an umbilical hernia.
Although low birth weight in this disorder is usually associated with premature birth, some neonates may be SGA. Assessment at birth may reveal these classic signs: petechiae and ecchymoses, jaundice, and hepatosplenomegaly, which increases for several days. The neonate may also have a high fever, lymphadenopathy, tachypnea, and dyspnea, along with prolonged bleeding at puncture sites.
Low birth weight and a wasted appearance occur in an SGA neonate. The neonate may be symmetrically short or may appear relatively long for his low weight. Additional findings reflect the underlying cause. For example, if maternal hyperparathyroidism caused placental dysfunction, the neonate may exhibit muscle jerking and twitching, carpopedal spasm, ankle clonus, vomiting, tachycardia, and tachypnea.
Usually, the low-birth-weight neonate with this disease is born at term but is SGA. A characteristic “blueberry muffin” rash accompanies cataracts, purpuric lesions, hepatosplenomegaly, and a large anterior fontanel. Abnormal heart sounds, if present, vary with the type of associated congenital heart defect.
The low-birth-weight neonate may be either premature or SGA and may have hydrocephalus or microcephalus. Associated findings include fever, seizures, lymphadenopathy, hepatosplenomegaly, jaundice, and rash. Other defects, which may occur months or years later, include strabismus, blindness, epilepsy, and mental retardation.
Low birth weight is accompanied by cataracts and skin vesicles.
To make up for low fat and glycogen stores in the low-birth-weight neonate, initiate feedings as soon as possible and continue to feed every 2 to 3 hours. Provide gavage or I.V. feeding for sick or very premature neonates. Check abdominal girth daily or more frequently if indicated, and check stools for blood because increasing girth and bloody stools may indicate necrotizing enterocolitis. A sepsis workup may be necessary if signs of infection are associated with low birth weight.
Check the neonate’s vital signs every 15 minutes for the first hour and at least once every hour thereafter until his condition stabilizes. Be alert for changes in temperature or behavior, feeding problems, respiratory distress, or periods of apnea—possible indications of infection. Also, monitor blood glucose levels and watch for signs and symptoms of hypoglycemia, such as irritability, jitteriness, tremors, seizures, irregular respirations, lethargy, and a high-pitched or weak cry. If the neonate is receiving supplemental oxygen, carefully monitor arterial blood gas values and the oxygen concentration of inspired air to prevent retinopathy.
Monitor the neonate’s urine output by weighing diapers before and after voiding. Check urine color, measure specific gravity, and test for the presence of glucose, blood, or protein. Also, watch for changes in the neonate’s skin color because increasing jaundice may indicate hyperbilirubinemia.
Encourage the parents to participate in their neonate’s care to strengthen bonding, and allow ample time for their questions.
Read excerpts from these other book chapters related to Stillbirth:
Copyright Details: Professional Guide to Signs & Symptoms (Fifth Edition), Copyright © 2008 Williams & Wilkins.
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More About This Book:
Title: Professional Guide to Signs & Symptoms (Fifth Edition) Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2006 ISBN: 1-58255-510-9 
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