Stratified and sensitivity analyses
In stratified analysis, we did not find any differential association of chronotype with odds of depressive symptoms, according to age, sex, annual income, education, passive smoking, physical activity, living children, infertility treatment time, cause of infertility, frequency of insomnia, nocturnal wake frequency, daytime napping, social jetlag, and nighttime sleep duration (all p  for interaction > 0.05). As illustrated in Figure 2 .
In addition, we performed repeated analyses to test the robustness of the results by excluding individuals who worked shift or night, the association of morning and neutral chronotypes with the risk of depressive status were similar to the main analysis (OR = 0.51, 95% CI: 0.30-0.87, P trend <0.001; OR = 0.32, 95% CI: 0.18-0.58, P trend <0.001, respectively). As illustrated in Table S2 .