“For the most part,” she said, “[in] most regions of the world there wasn’t very much change in infertility levels over time. But the big exception was actually sub-Saharan Africa, where we found there was a big decline in infertility levels. So primary infertility went from 2.7 percent of women in reproductive age in 1990 to 1.9 percent in 2010. And secondary infertility declined from 13.5 percent in 1990 to 11.6 percent in 2010.”

The study did not look into why infertility rates dropped in sub-Saharan Africa.

“We have some ideas, but we don’t have any proof. So some studies have shown that in sub-Saharan Africa one of the main causes of infertility is the effects from sexually transmitted infections, such as gonorrhea and chlamydia. One of our hypotheses is that perhaps some of the changes in behavior that have come about from the response to the HIV epidemic might have actually gone towards reducing infertility rates,” she said.

Such behavior change would include greater condom use and other safe sex practices. The WHO researcher says improved obstetric care may also be a factor. That’s because maternal mortality rates have fallen in sub-Saharan Africa. To be sure, however, Stevens said infertility studies would have to be conducted.

“Sometimes infertility is caused by female factors. Sometimes it’s caused by male factors and sometimes both. And I think that culturally in many regions of sub-Saharan Africa there’s been a tendency to blame the woman. But that shouldn’t be the starting point,” she said.