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Timely passage of the first stool is a hallmark of the well-being of the newborn infant. Failure of a full-term newborn to pass meconium in the first 24 hours may signal intestinal obstruction. Lower intestinal obstruction may be associated with disorders such as Hirschsprung's disease, anorectal malformations, meconium plug syndrome, small left colon syndrome, hypoganglionosis, neuronal intestinal dysplasia and megacystis-micro-- colon-intestinal hypoperistalsis syndrome. Radiologic studies are usually required to make the diagnosis. In addition, specific tests such as pelvic magnetic resonance imaging, anorectal manometry and rectal biopsy are helpful in the evaluation of newborns with failure to pass meconium. (Am Fam Physician 1999;60:2043-50.)
The first stool is passed within 24 hours of birth in 99 percent of healthy full-term infants and within 48 hours in all healthy full-term infants.1 Failure of a full-term newborn to pass meconium within the first 24 hours should raise a suspicion of intestinal obstruction. Among premature infants, however, one study2 revealed that only 37 percent of 844 preterm infants passed their first stool in the first 24 hours; 32 percent had delayed passage of the first stool beyond 48 hours. In 99 percent of the preterm infants, the first stool was passed by the ninth day after birth.
Clinical Presentation
of Meconium Retention
Failure to pass meconium combined with progressive abdominal distention, refusal to feed and vomiting of bilious intestinal contents are the classic clinical signs of intestinal obstruction in neonates. Abdominal examination often reveals distended loops of bowel, which may be visible or palpable. Anal inspection is essential to exclude the presence of anal atresia, perineal fistula with anal atresia, the membranous form of anal atresia and anal stenosis.
Plain radiographs of the abdomen do not allow differentiation of small bowel obstruction from large bowel obstruction. The differential diagnosis for small bowel obstruction in neonates includes duodenal atresia, malrotation and volvulus, jejunoileal atresia, meconium ileus and meconium peritonitis. Bilious vomiting, with or without abdominal distention, is usually the first sign of small bowel obstruction. The differential diagnosis for large bowel obstruction in neonates includes Hirschsprung's disease, anorectal malformations and meconium plug syndrome (Table 1).
In many cases of suspected neonatal intestinal obstruction, the clinical history and physical examination combined with plain abdominal radiographs, contrast enema radiographic examination,...