> Maybe I'm wrong, but it looks like the paper just has a misleading title, and this is about having children, not fertility.

I think the confusion is that “fertility” means different things in medicine vs demography

In medicine, fertility is about your ability to have biological offspring, not about whether you personally choose to make use of that ability

In demography, fertility is about how many children people actually have. The completed TFR (total fertility rate) of a population is the lifetime average number of children per a woman.

From a demographic perspective, the vast majority of differences in fertility are due to socioeconomic and cultural factors, medical infertility and the availability of treatments for it makes only very small difference to overall birth rates