Our first poo is called meconium and it starts to form during the second trimester, or at approximately 4-5 months, and by the time we were ready to be born it would have almost filled our colon. It’s a viscous, sticky, greenish-black substance that has little or no odour and should be completely passed within the first few days after birth.

Meconium serves a number of functions:

Interim Poo!
Acting as a stand in for poo during gestation, it allows the intestine to develop so it can digest milk immediately after birth.

Amniotic Fluid Filter!
Amniotic fluid serves many purposes and it ends up carrying many things within it that are undesirable, such as mucus, bile, fine hairs (called lanugo) and cells lining the inside of the womb. As the amniotic fluid is ingested, these items are stored and help form meconium. We covered amniotic fluid in more detail here: I’ve Drunk My Own Wee for Months, So Have You!.

Jaundice Minimiser!
A build up of bilirubin causes jaundice; Bilirubin is a by-product of the breakdown in red blood cells (we need far fewer once born than we did in utero) and is removed from the blood stream by the liver, accumulating in meconium. If it’s not excreted it can be re-absorbed into the baby’s system adding to the load upon an already immature liver, leading to jaundice.

 
Helping meconium on its merry way is colostrum, the first milk a mother produces. It comes in a quantity perfect for a newborn’s stomach and is packed full of nutrients and antibodies. Colostrum is also easily digested and has a laxative quality, perfect for helping get rid of meconium.

Holding your poo in isn’t fun at all once you’re older and no longer in utero! Here’s why you should avoid holding in your poo, check out this video from discovery news for reasons to avoid it.