When I get to the point where I don't have to worry about the family's bank account, I dose both parents with Baby Boost before each attempt to have a baby. I don't know if a doctor's consultation would have suggested the BB, but I reckon it can't do any harm. If you're as far enough in the game to have only a few collectibles to find, it's likely you won't have to worry about money, either.
It seems to work with me, as I've never had any families yet fail to produce any children, even if a couple of times the mother was in her late 40s before producing the first child. The oldest mother to have a baby for me was 51, but I/ve seen reports of 54 in the forums.
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To err is human; to arr is pirate.