Here we are in the 21st century and we're just figuring out how uterine contractions work.

Humans have giving birth for millions of years and we are only now unpacking part of the uterine contribution to this magic trick.

For years scientists used a rodent model to interrogate how uterine contractions work, which turned out to be the wrong model; scientists used the heart as a model organ to try to elucidate how electricity moves in the uterus and makes it contract, but that too, was the wrong model.

The uterus is sui generis, it's own unique organ that, according to Dr. Roger Young, is in the last decade, becoming better understood; His company is working on making a fetal monitor to better assess when labor is in fact happening, by measuring the pressure changes in the uterus, a statistic that's critical to understanding labor progression.  Keep listening to better understand how your uterus actually works.

To see some of Dr. Young's academic work: see https://pubmed.ncbi.nlm.nih.gov/?term=roger+young+uterus