Some claim
slight improvements. I have two views of this that I alternate between without coming to any lasting conclusion. In the first view, they've merely managed to move forward births that were always going to happen. Some couple would have a child two years from now, but because the governemnt (of whatever country) bribed them, they had the kid early. This isn't particularly difficult to eliminate by proper windowing, I thought, but they're often bragging about the numbers early and (of course) juking the stats.
In the second view, they have actually slightly increased fertility (and only temporarily). But at what cost? No one refuses to believe that it's impossible to bribe someone to have a child they wouldn't otherwise have anyway. If you offered $1 billion in cash, up front, you'd probably have riots of women trying to sign up for it. But this is ultimately unaffordable is it not? If the US needs 500,000 extra births next year, we can't afford $500 trillion for that, and not when we need as many the year after, and the year after that. It doesn't become more tractable by reducing the bribe, you get far few takers (which is why they've only managed to slightly raise fertility rates so far, they offered far too little).
Whichever of these possibilities happens to be the truth, neither bodes well. Government doesn't have any levers that it can pull to meaningfully change this.