More and more countries are joining the list. By 2100, just 12 countries — 11 in Africa and the tiny Pacific island state of Vanuatu — are expected to have fertility rates above the crucial level of 2.1 births per woman. Not a single country is expected to have a rate above 2.3 by the end of the century.

A McKinsey report in January suggested many of the world’s richest economies, such as the UK, US and Japan, would need to at least double productivity growth to maintain historical improvements in living standards amid sharp falls in their birth rates.

Women with low levels of education delay having children because of concerns about the stability of their relationships and the need to live near their parents. By contrast, those with a university education worry about dropping down the career ladder and want a hands-on partner, her research has suggested.

A Danish travel company even ran an ad campaign to “Do it for Denmark”.