Most newborns pass their first stool (meconium) within 24 hours of birth. 98 percent of infants will pass their first meconium stool within 48 hours. However, premature infants may have a delayed passage of meconium without any underlying problem.
A newborn who fails to pass stool within the first two days of life should be closely monitored and evaluated. This may involve a physical examination to rule out anorectal malformations or any other underlying problems. Several diagnostic techniques may be performed including a biopsy or water-soluble contrast enema to evaluate for conditions such as small left colon syndrome, meconium ileus (when stool is blocking the small intestine), meconium plug syndrome or Hirschsprung disease.
If no anatomical issues are present, the cause of functional constipation in infants is typically around the time of transition from breast milk to formula or to the introduction of solid foods. An infant may have hard stools that are difficult and painful to pass. This traumatic experience may result in voluntary withholding of stool. This behavior is characterized by grunting, arching of the back, stiffening of the legs and the body.
Infants with functional constipation may respond to the addition of fruit juices to their diet, such as prune juice. Changing formula (especially if the current formula contains iron) may be helpful. Some solid foods that are introduced to the infant’s diet such as rice cereal, bananas, or applesauce, may also be constipating and should be avoided.