Most advanced countries do not have a self-sustaining birth rate (above 2.1, the replacement rate). Some are able to make up the difference in immigration, but

Most advanced countries do not have a self-sustaining birth rate (above 2.1, the replacement rate). Some are able to make up the difference in immigration, but immigrants assimilate and then the birth rates go back down. The US is at 1.77, Canada at 1.5, UK 1.79