According to data from the National Bureau of Statistics, the number of newborns in China in 2017 was 17.23 million, and the sampled fertility rate was 1.58. Although the fertility rate does not seem low, in fact, the fertility accumulation brought about by the second-child policy has pushed up the fertility rate. The fertility rates for first-child, second-child, third-child, and above were 0.67, 0.81, and 0.11, respectively. It can be seen that the fertility rate of the second child is even higher than that of the first child, accounting for more than half of the total fertility rate. Since one must have given birth to the first child before having the second child, when the fertility situation stabilizes, the fertility rate of the second child will inevitably be lower than that of the first child. If we remove the second-child accumulation factor, even if we assume that up to 60% of mothers who have given birth to one child will give birth to a second child, the total fertility rate in 2017 would only be 1.18 (i.e., 0.67 + 0.6 * 0.67 + 0.11).
This trend became even more pronounced in 2018. Although the sampled fertility rate for 2018 has not yet been released, the fertility rate estimated from the 15.23 million births reported in the statistical bulletin is only 1.46, a 10% decrease from the 1.63 in 2017. In 2017, the number of second children was 1.22 times that of the first child, and the second-child fertility rate was 1.21 times that of the first child, with the two ratios being similar. However, in 2018, there were still more second children than first children, meaning that the second-child fertility rate was at least roughly equivalent to the first-child fertility rate. That is, about 1/4 of the total fertility rate of 1.46 in 2018 can be attributed to accumulation. If we remove the fertility accumulation factor, the natural fertility rate in 2018 is only about 1.1. If the fertility rate remains at 1.1 for a long time, it means that the number of births will be halved every generation.