Newborns (for the first two or three days) will pass meconium, a sticky, greenish-black material that once filled their intestines in the womb. Then their bowel movements will change in color and consistency, depending on whether they're breastfeeding or on formula. Infants typically have between three and nine bowel movements a day (it varies with how much they eat).
Formula-fed babies pass yellow to tan stools that have a peanut butter-like consistency and a particularly foul smell. After 2 months of age, bottle-fed infants may poop as often as five times a day.
Breastfed babies often have yellow, soft stools with small, seed-like particles. (A greenish-tinged stool is normal, as long as the baby is eating and gaining weight.) Expect as few as two bowel movements a week after 2 months, as a mother's production of colostrum (which some researchers suspect is a natural laxative) starts to taper off. Breast milk also tends to be more easily digested and leaves hardly any solid waste.
Call a doctor if your baby hasn't pooped in more than three days; develops diarrhea; or passes black, white, grey, or bloody stools, which may indicate an infection or blocked intestine.