Covariates
All covariates were derived from self-reported baseline questionnaires.
We searched the previously relevant literature and used a directed
acyclic graph to select potential confounders35(Figure S2 ). Specifically, the following covariables are
considered in the analysis: age (≤29, 30-34, and ≥35 years), sex (male,
female), annual income (<30,000,
30,000~60,000, ≥60,000), education (middle school or
below, high/ vocational school, college degree or above), passive
smoking (never, occasionally, frequently), physical activity (low,
moderate, vigorous), living children (yes or no), infertility treatment
time (≤6, 7~12, 13~24, >24
month), cause of infertility (male, female, both, and unexplained),
frequency of insomnia (never, occasionally or ≤3 per month, ≥4 per
month), nocturnal wake frequency (never, occasionally, ≥1 per night),
daytime napping (never, <1 and ≥1h ), social jetlag
(<1 and ≥1h), and nighttime sleep duration (<8 and
≥8h).