10 Things You Never Knew About Meconium

1. It's poop! Meconium is a fancy name for a newborn infant's first stool.

2. There's hair in there. The very first poo your baby passes doesn't contain breast milk or formula just yet. Instead, it's jam-packed with materials your baby ingested in utero, like skin cells that have been shed, mucus, amniotic fluid, bile, water, and lanugo, which is the fine, soft hair that covers baby's body.

3. It's greenish black. Baby's first BM is viscous and sticky, thick, and a super-dark (almost black) greenish black. Essentially, your newborn's poop is greenish black tar.

4. There's no stink. It's disgusting, for sure, but it carries no vile aroma. Win!

5. It clings to baby's skin. Thanks to meconium's high viscosity, it can cling to your baby's buns (and, let's face it, back) like nobody's business. The trick to an easy cleanup is to apply a thin coat of petroleum jelly to your newborn's clean dry skin before the poop flies. This pre-poop lube helps the meconium slide off with minimum elbow grease.

6. It's sterile. It's believed that the very first stool to leave your newborn is free of bacteria because her teeny intestines have yet to be colonized by microorganisms.

7. It doesn't last long. By definition, a baby's first poops can't stick around for too long. Generally, infants continue to pass meconium over the first day or so. Next up: greenish-brown poop, followed by yellow-y stuff that smells bad and has the consistency of diluted Dijon mustard. (Breastfed babies' BM may also have small white bits that resemble seeds.)

8. It can be passed in utero. Up to 25 percent of newborns simply can't wait to have their first poop and do it in the womb—or on their way out. This pre-birth poop taints the color of the amniotic fluid, which gives health-care pros a heads-up that meconium has passed. The doc or midwife can then monitor the baby carefully to ensure that he doesn't develop any complications.

9. There's an inhalation risk. When poop is passed in the womb, there's always a chance your unborn baby will inhale it. This complication, dubbed meconium aspiration syndrome (MAS), is rare in babies born before 34 weeks. But once your baby is overdue, her risk ekes up. MAS can also happen before, during, or after labor and delivery, when a newborn inhales a mixture of meconium and amniotic fluid, which can partially or completely block the airways.

10. It may thwart your water birth. While there are no hard-and-fast rules about laboring in a tub after meconium is present, many pros will put the kibosh on the practice. The reason: Your birthing team will want immediate access to your baby to be able to clear his airways if needed.