One of the most horrendous ironies of WW2 is that we actually learned so much about human body through the Nazis horrific experiments, with sterilisation and birth control being of particular interest. I recall reading about a machine they developed that basically microwaved a dude's testicles without him realising. So that tech has existed for good 80 years now, but the invasive and cruel fertility experiments on women continue, which means its never really about keeping a potential population down, and all about making sure the current one knows its place.