The first type of stool your newborn will have is called meconium. It is dark green in color, and a thick, sticky consistency (a little thicker than jelly). Some babies will pass meconium in utero; this is more common in babies who are born after their due date. Most babies will start having meconium stools in the first 48 hours of life. They typically last for a day or two, before turning into soft, yellow-green transitional stool.