M is for Meconium

Meconium is the first substance that occupies your baby’s bowels. Unlike stools that will form and be passed after baby has begun eating, meconium is composed of substances your baby ingested in utero, including: skin cells, lanugo (the fine hair that covers their body in uter0), amniotic fluid, bile (responsible for the coloring of meconium), and water. It is thick, sticky, and almost odorless.

What do I need to know about meconium?

  • Meconium isĀ sticky. For this reason you may want to apply a barrier to baby’s bottom to make clean-up a bit easier. We do not recommend Vaseline or other petroleum products. Coconut oil is a safer alternative.
  • Meconium is only passed for the first 1-3 days after birth.
  • It is sterile and does not contain bacteria – that is the primary difference between meconium and stool.
  • It can be passed in utero which has the potential to be dangerous.
    • If your baby passes meconium in utero it could indicate that your baby is post-date (and ready to be born) or that your baby is in some form of distress (such as maternal high blood pressure, low oxygenation, placental insufficiency, oligohydramnios, infection, etc).
      • Low blood-oxygen levels cause baby’s muscles to relax, which may be the cause of the pre-delivery bowel movement.
      • If your water breaks and it is mostly clear with some greenish-black specks, your baby likely recently passed his first stool. This causes less of a concern than if your water breaks and it is homogeneously greenish. This is indicative that more time has elapsed since your baby passed the meconium and your baby is at a greater risk of complications.
      • EITHER WAY: If your amniotic fluid is anything other than straw colored (some blood specks are normal), call your OB or midwife immediately and go straight to the hospital. Note the time your water broke and the color.
  • Your placenta can still be encapsulated if your baby has passed meconium in utero.

Is Meconium Aspiration Syndrome (MAS) something I should worry about?

MAS occurs when baby inhales meconium in utero. It can potentially block their airway, leading to trouble breathing. This blockage may be cleared by a medical provider with a bulb syringe or, in more severe cases, a breathing tube. When the airways are blocked, the trapped air has the potential to cause hyperinflation of the lung resulting in hyperexpansion of the alveoli and increased resistance during exhalation. The resistance during exhalation is caused by the meconium deactivating surfactant, which normally lubricates the lungs.

In the US, meconium-stained amniotic fluid is detected in 8-25% of births occurring after 34 weeks. Of these babies, about 10% of them develop MAS (so, approximately 1.5% of all births). More information on MAS can be found here.


The information in this article is not meant to diagnose, treat, cure, or prevent any disease. Reading this article should not take the place of consultation with your healthcare professional.


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