The World Health Organization says infertility rates around the world have remained relatively stable since 1990. Almost 50 million couples worldwide were unable to have a child after five years of trying. However, one region was a big exception. The WHO says infertility rates have declined in sub-Saharan Africa.

“This study is measuring infertility rather than fertility itself. And the reason that we set out to try to determine what infertility levels were is because we found that it’s a bit of a neglected area of reproductive health, said WHO statistician Gretchen Stevens, who led the study on infertility rates.

It analyzed hundreds of household surveys in 190 countries from 1990 to 2010. She says it took a different approach than previous research.

“In general, people have worried quite a bit about getting people access to contraceptives so that they could prevent unwanted pregnancies. But they haven’t worried as much about when couples are trying to become pregnant and aren’t able to do so. This is actually a first study that looks at trends in infertility worldwide and in different countries. And we thought that this might be able to raise the profile of the condition,” she said.

The results were published in PLOS Medicine, an open access medical journal. The study measured primary infertility – the inability of young women to have their first live birth – and secondary infertility – the inability the have another baby.

“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.

Stevens added that she was surprised that the overall findings showed global infertility rates remained very stable. That’s because in higher income countries there’s been concern about environmental factors affecting sperm quality and about a growing number of older women having children. But the study found no evidence to support those factors affecting infertility rates.