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.