Embryo
Fetus, Foetus
noun, の adjective
A child that's still in a womb is a fetus.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
エコーで胎児が足を伸ばしたり縮めたりするところが見れました。
I was able to see the fetus stretch and shrink on the echo.