No country resorts to IVF more than Japan—or has less success

The sterile façade of Kato Ladies Clinic gives little hint of the fecundity inside. Nestling among a plantation of high-rises in a business district of Tokyo, the clinic implants fertilised eggs in an average of 75 women a day. That makes it one of the busiest fertility hospitals in the world, says Keiichi Kato, the medical director.

Japan has come a long way since journalists were warned off the taboo story of Princess Masako’s visits to fertility clinics 20 years ago. The wife of the crown prince, then in her late thirties, was being nudged to produce an heir to the throne (in the end, she disappointed traditionalists by having a girl). Today Japan has less than half America’s population, but more than a third more hospitals and clinics that offer fertility treatment. Over 50,000 babies were born last year with the help of in vitro fertilisation (IVF)—5% of all births.

Nearly a fifth of Japanese couples struggle to have children, says the health ministry. Women are postponing marriage; social pressures mean there are far fewer babies born out of...