What about the difficulty of having 12 pregnancies? You'd have to set aside 12 years in the first place. A woman in such a family isn't planning on working.
Women don't need to be off work for the entire pregnancy nor the entire year after giving birth, though. If you are splitting your maternity leave with your spouse, you might not take an entire year off. You might just take the time that pays you more instead of being paid less: I don't know how it is other places, but you aren't getting paid for maternity leave if you don't work. (IIRC, in norway, the man doesn't get much leave if the woman isn't working).
Your job is probably protected while on maternity leave too.
I*d say that one of the main difficulties with 12 pregnancies is the actual pregnancies - they are hard on the body and honestly, it isn't recommended that folks have a pregnancy a year - if one even is able to have so many. The more likely situation is that having 12 children means some of those children are fosters or adoptions. And at that point, I don't actually care if someone has 12 children so long as they are good parents.
