The secret to getting pregnant: Ingesting a parasitic worm.

A study of 986 indigenous women in Bolivia found that those infected with a certain type of roundworm — the Ascaris lumbricoides — on average gave birth to two children more than women not infected, Science magazine reports.

The typical family size for Tsimane people, who live in the Amazon rainforest, is nine children. Almost 70 percent of the population tested positive for a parasitic worm infection during the nine-year study.

According to researchers, the worm may be altering women’s immune systems, making it easier to both become pregnant and carry a pregnancy to term.

A second parasite, hookworm, was also detected in the population and has an opposite effect on its host. Women who tested positive for hookworm had three fewer children than average.

The discoveries of both parasites could prove invaluable for fertility-enhancing drugs — although experts warn that women struggling to get pregnant shouldn’t seek out the parasite until further research has been conducted.