• Question: How is the placenta formed?

    Asked by to Paul, Gill on 7 Jan 2019. This question was also asked by .
    • Photo: Gill Harrison

      Gill Harrison answered on 7 Jan 2019:

      I’m guessing Paul might be better placed to answer this. My experience is looking at the placenta within the uterus (womb) and seeing if it looks to be in a good position or not – that is whether it is close to the birth canal (intern os) or not. If it is covering the birth canal, this can cause complications for the pregnancy and might prevent a normal delivery. I also look to see where the cord is inserting into the placenta, to see if that looks normal. If it is at the side rather than central, it might cause other problems with the pregnancy or you can find vessels that block the baby’s exit route.

    • Photo: Paul McKeegan

      Paul McKeegan answered on 11 Jan 2019:

      Wow! My expertise is in the very first stages of embryo development, so I don’t spend much time on the fully grown placenta. I am learning a lot about the placenta myself recently as several of my colleagues are researching it!

      In the first week following fertilisation, the embryo is about 1/100th of a millimetre across. It divides, creating more cells, but the whole embryo stays the same size and the cells get smaller and smaller. When you get to about 100 cells, the embryo starts to form different types of cells for the very first time. It squishes down, then starts to fill up with water to make a fluid called the blastocoel (“blast-o-seal”). Some of the cells stay together in a clump and these go on to form the fetus, while the other cells around the outside of the embryo will instead eventually form most of the placenta. The embryo sticks to the side of the womb and over the next few weeks forms the different types of cells needed to make the fetus and the placenta. So the placenta is mostly formed by the embryo!

      The placenta develops along with the embryo throughout the rest of the pregnancy, and links up with mum’s blood supply to bring oxygen and nutrients into the embryo. It is really important for the development of the baby. It is itself formed of several layers of different cells and looks really different to other organs in the body.

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