Meconium typically lasts about two to three days after birth. Most healthy full-term newborns pass their first meconium stool within 24 hours of delivery, and by days three to four, the dark, tarry stools give way to lighter transitional stools as your baby begins digesting breast milk or formula.
What Meconium Looks Like
Meconium is distinct from every other diaper you’ll change. It’s thick, sticky, and dark green to black, with a tar-like consistency that can be surprisingly difficult to wipe off your baby’s skin. Unlike later stools, it’s nearly odorless.
That’s because meconium isn’t digested food. It’s a collection of everything your baby swallowed in the womb: water (up to 80% of its content), mucus, digestive enzymes, shed skin cells, fine hair, and bile pigments that give it its characteristic dark green color. Your baby’s intestines begin accumulating this material as early as 13 weeks of pregnancy, so by birth there’s a substantial amount to clear out.
The Typical Timeline
In 99% of healthy full-term newborns, the first meconium stool passes within 24 hours of birth. Virtually all full-term babies will have passed meconium by the 48-hour mark. From that first stool, most babies continue passing meconium for roughly two to three days before it transitions.
Premature babies follow a slower schedule. Only about 37% of preterm infants pass their first stool in the first 24 hours, and nearly a third take longer than 48 hours. For preterm babies, it can take up to nine days before that first stool appears, so a longer meconium phase is expected.
Transitional Stools: The In-Between Phase
You won’t see a clean switch from meconium to normal baby poop. Instead, there’s a transitional period, usually around days three through five, where stools shift from black-green to a yellow-green color. The consistency loosens, and you’ll start noticing a more seedy or curdled texture if your baby is breastfed, or a slightly firmer, tan-colored stool if they’re on formula.
This transition happens faster in breastfed babies. Colostrum, the concentrated early breast milk produced in the first few days, acts as a natural laxative that helps your baby flush meconium through the intestines more quickly. It comes in small volumes, but its laxative effect is potent enough to clear the digestive tract and prepare it for processing mature milk. Early and frequent breastfeeding in the first hours after birth speeds this process along, which is one reason lactation support teams encourage putting baby to the breast as soon as possible.
When Meconium Takes Too Long
If a full-term baby hasn’t passed meconium within 48 hours, medical teams will investigate. Delayed passage can signal an intestinal blockage or an underlying condition. Cystic fibrosis is one condition closely associated with delayed meconium, sometimes presenting as meconium ileus, where thickened meconium physically obstructs the intestines. Meconium plug syndrome, where a hard plug of meconium blocks the lower bowel, is another possibility.
These conditions are uncommon, but the 48-hour threshold exists because early detection makes a significant difference in outcomes. If your baby is straining without producing stool, has a visibly distended belly, or is vomiting green fluid, those are signs the medical team needs to evaluate promptly.
Meconium Before Birth
Sometimes babies pass meconium while still in the womb, staining the amniotic fluid. This occurs more often in babies who are past their due date or under stress during labor. The primary concern is meconium aspiration syndrome, where the baby inhales the stained fluid into the lungs during delivery.
When meconium is present in the amniotic fluid, delivery teams watch closely for signs of respiratory distress. Among babies born through meconium-stained fluid, roughly 3% to 7% need respiratory support after birth, depending on when during labor the meconium was released. Most babies born through lightly stained fluid do perfectly well, but the medical team will monitor breathing and oxygen levels closely in the first hours.
Meconium and Drug Testing
One aspect of meconium that surprises many parents is its role in toxicology screening. Because meconium accumulates over months in the womb, it can be tested for substance exposure during pregnancy. The detection window covers approximately the last trimester of a full-term pregnancy, making it a longer lookback than blood or urine testing of the newborn. Hospitals may collect meconium for this purpose when there are clinical concerns, and the sample needs to be gathered within those first two to three days before meconium transitions to regular stool.