It seems very likely to my mind that producing a male child would probably exempt a woman from being drafted into the guard but maybe it should be two. If you really wanted to make a dark and horrible setting there's a lot of room for horrors down that road. As GW seems intent on making Warhammer 40k a popular mainstream property it seems unlikely they will ever go there.
Turning women into birthing tanks is a cliché. It's no longer horrifying or even surprising. It's normal and expected now. If women appear in speculative fiction, then they're probably going to be subjected to rape or forced birth because that's just how women are treated. It's an inevitability of being a woman. Even leftists acknowledge this in real life by literally referring to them as "uterus havers" nowadays.
Here's my suggestion to update it for modern times and the technological capabilities of the setting: all soy boys, transwomen, non-binaries, etc get implanted with uteruses and turned into birthing bodies too. The only people that serve in the guard are ultra alpha men with roided up bodies.
It seems very likely to my mind that producing a male child would probably exempt a woman from being drafted into the guard but maybe it should be two. If you really wanted to make a dark and horrible setting there's a lot of room for horrors down that road. As GW seems intent on making Warhammer 40k a popular mainstream property it seems unlikely they will ever go there.
The Vostroyan Firstborn regiments have a tradition which involves newly minted regiments of men getting hooked up with girls for a night, so that they can sire another generation.
And that's on the nicer side of the spectrum. Pretty sure the Death Korps of Krieg uses vat-grown children to fill out its ranks.
Cloning vats are honestly much easier to care for than birthing bodies. They don't need to be prepared with lobotomies and amputations (or uterus implants in the case of repurposed non-alpha males), they don't produce piss and shit that you need to constantly clean up, etc.
Honestly, it's more efficient to just get rid of all the women entirely and use cloning vats instead.