I said unwise, not impossible, and I chose the word with care. 10% matters enormously if you are trying to squeeze a human baby's head through it while doing as little damage as possible. The engineering of the human female pelvis is a very unfortunate compromise between running and childbirth, and tolerances are... tight.

Living arrangements have bewildering diversity across cultures, there is no 100% on anything, but I'm on safe ground when I say the overwhelming majority of extant cultures that practice early female marriage also overwhelmingly practice both both patrilocalism and multigenerational households. 

 Feel like with today's medical procedures, that 10% can be easily circumvented. Also, would love to see some data on how 12 yo girls giving birth somehow causes vaginal fistula.
Bear in mind, if you are Catholic, you have to belief Mary gave birth to Jesus when she was at most 14, as was the Hebrew tradition for girls to marry at ages 12-14. Now what, were they all running terrible risks? 

 And yes, multigenerational household, that I agree with, but not with the notion that the husband needs to move in to the wife's house. Rather, I saw cases where it's the opposite.