See that bulge in women between 33 and 40? In five years, they’ll be out of the childbearing business. Then China will be left with the smaller number of women born between 1995 and 2010.
The women between 33 and 40 are probably not having children. Most likely the drop that we see now reflects both the smaller 20 to 33 cohort of women, as well as the low number of babies/mother.