Infants will pass a thick, green-black stool (meconium) in the first 24 to 36 hours of life. As feedings become established, the stool becomes more yellow-green. Most infants have stools daily, but some have them only every two to three days. If that infant is feeding well, has soft stools and isn't uncomfortable, she's probably not constipated.

Formula-fed babies tend to have drier, less frequent stools than breastfed babies. Breastfed babies are rarely constipated. Just after birth it seems they have a stool every time they eat. But after a few weeks the pattern can change to a stool every two or three days or even once a week. If the baby is not uncomfortable and the stools are soft, there's probably no problem.

Even if your baby strains to pass a stool, he may not be constipated. Babies often grunt, become red in the face and pull up their legs when passing a stool. If it's soft and passes without pain, these behaviors are normal. If your infant appears to be having difficulty, curling the knees up against the baby's chest might help.