The relationship between silicon wafer fabrication room (fab) work and fecundability were investigated. The women participating in the study included 481 who completed baseline interviews of the 739 who had been declared eligible to participate. In the 2 hours interviews, participants offered information on sociodemographic characteristics, medical and reproductive histories, habits (such as alcohol, caffeine, and tobacco use) job activities and exposure, work shifts, occupational stress, and current job duration. They collected 5 milliliters of urine each day on awakening and they also completed a daily diary which took about 5 minutes to complete a day. The diaries included information on whether they had had menstrual bleeding, contraceptive use or intercourse. Diaries also included questions about activities at work and elsewhere. A total of 403 women completed at least one menstrual cycle of diary entries and urine collection. The women were phoned once a month and at the end of the month to determine any change in work activities, eligibility, or pregnancy status. A total of 152 fab workers contributed 736 cycles and 2,561 nonfab workers contributed 1,179 cycles. Pregnancy occurred in 2.6% of the menstrual cycles of fab workers and 2.8% of the cycles of nonfab workers. The results indicated that fab workers, and particularly dopant and thin film workers, have a lower probability than nonfab workers of becoming pregnant in each menstrual cycle. The authors conclude also that women exposed to ethylene based glycol ethers (EGE) have somewhat lower fecundability than women unexposed to EGE.