I would like to know the origins of the placenta. I know it’s a weird question, but I have never understood how the placenta stays in the same place throughout pregnancy. Thank you for your answer. Amelia

Amelia, the placenta forms when a fertilised egg (ova and sperm) arrive in the uterus to nest in the mucous membrane inside the uterus. At the location where the egg implants itself, the placenta will form, and gradually over a period of four weeks will allow for circulation between the mother and baby so it can feed and eliminate waste.

The placenta doesn’t change its location on the walls of the uterus during pregnancy, but it follows its expansion. You might see it change position over time during different ultrasounds. This is why marginal previa (near the cervix) identified during the 20-week ultrasound may have moved upwards when re-evaluated during the 32-week ultrasound.

I hope this short answer has helped, and if you want more information, please read my article called Let’s Talk Placenta.


Talk soon,



The Baby Expert

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