While Ascaris lumbricoides increased fertility, an infection with hookworm had the opposite effect, leading to women having three little children.
Another fertility scientist, professor Allan Pacey at the University of Sheffield, said the results could lead to new drugs for women wanting to become pregnant.
These women have been reported as the most fertile around the world -as they have an average of 10 children in their lifetimes-, an assumption that lead researchers from the University of California to investigate this phenomenon.
Infection with roundworm was associated with earlier first births and shortened inter-birth intervals, but infection with the hookworm was associated with delayed first pregnancy and extended inter-birth intervals.
He said women's immune systems naturally changed during pregnancy so they did not reject the fetus. He added that more research would have to be carried out before considering the "intriguing possibility" that the worm could be used to increase fertility. However, he warned that there was far more work to be done "before we would recommend anyone try this".
Different species of parasitic intestinal worms could affect when the next pregnancy of a Tsimane woman would be. As per the study, Ascaris lumbricoides help in boosting a woman's fertility so that she conceives.
The study, of 986 Tsimane women in Bolivia, found most couples there have nine children.
Bacteria and viruses try to overwhelm the immune system by multiplying rapidly.
First of all, the results are very preliminary, they only show an association rather than a causal link, and researchers don't know what mechanisms may be at play.
"This study examines yet another domain where helminths and their regulatory effect on the immune system may be relevant to broader aspects of health and well-being", said Michael Gurven, an anthropology professor at UCSB, in a press release. Furthermore, the high fertility rates lead to a population growth of approximately 4 percent per year.