Probably a bit of both? It says that women are having their first child at the age of 33.6, the oldest in the OECD. The older you have a child the more difficulty you will have so they also put money into fertility clinics. This means low fertility rates.

It’s not necessarily a health issue on a mass scale but an economic issue driving people to delay having children until they feel they can handle the responsibility. This causes low birth rates below 1.