Interesting thing is that according to some sources the world population has slowed its yearly increase. All over the world women are having fewer children than they had a few decades ago. No one seems to know just why.
Maybe not the -exact- reason but there's a number of pretty solid theories. Most have been determined in the course of China's zero-growth policy, set in 1979, and that's been plenty of time to study the success and failure of changes in the policy. The majority of economists and sociologists seem to have roughly agreed that the predominant impact on birthrate is that of a shift in women's priorities and options.
Women in industrialized, first world nations have fewer children; China's experience has shown that as women have opportunities for better jobs, higher-paying jobs, education, travel, material goods, etc, children become seen as a another potential drain on familial resources. The two-income parents, then, say: 'if we have a child, we lose what we've gained in two incomes' - contrasted to families where the woman is expected to stay at home, so why not have children/raise them as long as that's where you're stuck?
Then again, I'm also pondering a story in which artificially created, externally controlled circumstances keep an area of the population from reproducing above a certain rate. That means this topic is at the forefront of my gray matter, along with wormholes...and how vacuum cleaners work. Don't ask.
Getting back on topic, I'd say that what makes the science implausible often makes the story itself implausible. Nothing does that trick faster than a lack of research, and it does show in one's writing. But then, I've cultivated friendships with folks in some pretty wacky disciplines, and have trained them to not blink when I say, "okay, so it's not feasible in your experience, but what would it
take to make it work? What do I have to jury-rig?"
A good jury-rigging will make even the most implausible science believable to those of us who don't know, and at least mildly palatable to those who do.