Of 800 Danish women followed for the study, 261 tried treatments including reflexology, herbal supplements, homeopathy, kinesiology and acupuncture.
The women using such treatments overall were 20 percent less likely to get pregnant than those who did not, according to researchers Dr. Jacky Boivin, of Cardiff University, and Dr. Lone Schmidt, from the University of Copenhagen.
"Doctors tend to think that these kinds of therapies are benign," said Boivin, who was surprised by the results. "But maybe they're not as benign as we think they are."