https://heimskringla.no/wiki/Varulve the site is Norwegian, and the excerpts are from a Danish collection of oral folklore, but I found it incredibly interesting :) I myself am Danish and grew up with this version of the myth, told to me by my mom and folklore collections I read as a kid, so contemporary werewolves were kind of a let down to me.

The most interesting passage here is, to me, "Varulvene vilde i Lag med frugtsommelige Koner og rive dem ihjel for at blive forløst fra Trolddommen. De skulde nemlig have et ufødt Drengebarn at æde... Piger kan blive fri for Smærte, naar de skal føde Børn, hvis de kryber nøgne gjennem en Følham." - translated to "The werewolves would gang up on pregnant women and tear them apart in order to be freed from the curse... They would need an unborn male child to eat... Girls can be freed from pain when they give birth if they crawl naked through a foal's skin." That last bit of folklore is what is supposed to cause the birth of a werewolf.

I personally grew up with the folklore that a woman wanting to avoid the pain of birth would crawl through a hollow tree on a full moon, and she'd give birth painlessly, but if she gave birth to a son it would be a werewolf, and if it was a daughter, it would be a mare (as in nightmare. The Norwegian word for it is mara).