America even managed to reach the replacement rate of 2.1, meaning its population was sustaining itself, without taking migration into account.

美国甚至达到2.1的人口置换率，这意味着，在不考虑移民的情况下，该国人口基本保持不变。

The pattern of swift, uninterrupted decline is now taken as the norm: the UN uses it to project a worldwide convergence towards the replacement rate of fertility (2.1, the rate at which a population stabilises in the long term) .

现在，生育率快速连续的下降趋势已被人们视为正常：联合国用这种趋势来表示世界性趋同的人口替换率（2.1，人口长期稳定时的人口增长速率）。