This has easily offset the general decline in the birthrate of advanced countries.

发达国家的出生率的普遍降低被轻易抵消。

The birthrate is on the decline.

出生率在下降。

Other factors have also played an important part in the decline of the US birthrate in the past decade, including the aging of the population.

其他导致美国人口出生率降低的因素也起了很重要的作用，包括人口的老龄化。