a Adjustments included age, ethnicity, educational level, employment status, history of toxic exposure, smoking and drinking status of couples, frequency of physical exercise in women, annual household income of the family, duration of cohabitation (years), menstrual cycle interval, history of abnormal pregnancy, and parity.
b Represents participants’ age when they started attempting to conceive.
c Included clerk, professional worker, service worker, agricultural and related worker, and factory worker.
d Restricted to radioactive and toxic substances.
e Represents the duration of cohabitation when couples started attempting to conceive.