Meconium may also form plugs in the large intestine or anus, causing a temporary blockage. Babies who have meconium ileus almost always develop other symptoms of cystic fibrosis later. The first symptom of cystic fibrosis in an infant who doesn't have meconium ileus is often poor weight gain at 4 to 6 weeks. Inadequate amounts of the pancreatic secretions essential for proper digestion of fats and proteins lead to poor digestion in 85 to 90 percent of babies with cystic fibrosis. The baby has frequent, bulky, foul-smelling, oily stools and may have a protruding abdomen.
Growth is slow despite a normal or large appetite.
The baby is thin and has flabby muscles. In 20 percent of untreated infants and toddlers, the lining of the large intestine protrudes through the anus, a condition called rectal prolapse. Babies who have been fed soy protein formula or breast milk may develop anemia and swelling because they aren't absorbing enough protein. About half the children with cystic fibrosis are first taken to the doctor because they keep coughing, wheezing, and having respiratory tract infections. Coughing, the most noticeable symptom, is often accompanied by gagging, vomiting, and disturbed sleep.