According to a new study, women who have higher blood levels of flame retardants, called PBDEs found in several household articles took almost twice as long to get pregnant as those who had lower blood levels.

Study researcher Kim Harley, PhD, said that every tenfold increase in PBDEs in the blood lead to a 30-50 percent decrease in the odds of becoming pregnant in any given month.

Kim is also the adjunct assistant professor of maternal and child health and associate director of the Center for Children’s Environment Health Research at the University of California Berkeley School of Public Health.

The study appears online in Environmental Health Perspectives. A spokesperson for the industry said that the findings of the study are limited to PBDEs which are not used in new production. He also said that the environmental levels of those PBDEs are expected to decline over time.

The exact affect of chemicals deciding the time of pregnancy is not known, but experts say that disrupted thyroid functioning may be one of the reasons. Normal menstrual patterns can be altered by low or high thyroid levels affecting fertility.