Now that I think about it, the fertility of lower classes could be decreased by giving out contraception for free and subsidizing abortions, but the latter could be very unpopular. (It shouldn't affect the fertility of upper classes because the price of contraception/abortions isn't one of the reasons why they're not having fewer children.)

(Why was the parent downvoted, BTW? I guess because the downvoter thinks continental Europe/Japan are already overpopulated so sub-replacement fertility there is not bad.)