A much bigger reason for low births is insane housing costs. The price-to-income ratio in cities like Shanghai or Beijing make even London look cheap by comparison. Who is going to have kids if you can't afford big apartments and/or houses relatively easily?
Another issue is lack of religiosity. Religion drives fertility. For an atheist nation there are hard limits. Maybe China can get to Japan's 1.4 TFR from today's 1.1. The key issue should be to avoid rock-bottom TFR like South Korea's 0.8 TFR.