“For many, many years, we only talked about safe sex, how to prevent getting pregnant,” said Marianne Lomholt, the national director of Sex and Society. “Suddenly we just thought, maybe we should actually also tell them about how to get pregnant.”

The demographic shift is more pressing in Europe than almost any other major region, save Japan. There are an estimated 28 Europeans 65 or older for every 100 residents ages 20 to 64, almost twice the world average, according to the United Nations, and compared with 24.7 for the United States. By the end of the century, the United Nations expects the European figure to double.

Such trends will transform societies, potentially reducing economic growth and increasing stress on public pension systems and requiring more elder care. Japan already faces existential questions in a country where adult diaper sales are beginning to eclipse those of baby diapers.