Participants
From August to October 2022, we conducted this cross-sectional study among infertile couples in an artificial endometrial preparation from the Center for Reproductive Medicine, First Affiliated Hospital of Anhui Medical University (Hefei, Anhui, China). Those patients who met the diagnostic criteria for infertility and were actively seeking treatment were included. Subjects with a history of psychiatric disease, no embryo transfer, comorbidities such as hypertension, diabetes, or kidney disease, or voluntarily withdrew were excluded (n = 152). In this study, baseline data were collected on the day of the ovulation injection through a questionnaire that the subjects scanned a QR code using a mobile application to access the questionnaire and completed it under the constant supervision of highly trained research staff. The content of the questionnaire included general demographic characteristics (age, sex, ethnicity, education level, income, occupation, and marital status), behavioral lifestyle (smoking or passive smoking, alcohol and coffee consumption, Sleep, psychological state, physical activity, and dietary habits), family and social relationships (social capital, family power and reproductive quality of life) and fertility treatment history (parity, gravidity, history of preterm birth and abortion, infertility treatment timing and causes). Ultimately, after subjects with missing data were excluded (n = 44), a total of 1,022 infertile patients were included in the final analysis. The study protocol was approved by the Ethics Committee of Anhui Medical University (No. 20200961) in accordance with the guidelines of the Declaration of Helsinki and international ethical standards. All invited participants have obtained a written informed consent form to participate in the study (Figure S1 ).
Chronotype assessment
At present, the most widely used circadian rhythm scale is the Morning and Evening Questionnaire, of which the Morning and Evening Questionnaire-19 Items (MEQ-19) was first proposed by Horne and Ostberg 31. In order to quickly screen the chronotypes, we used the Morning and Evening Questionnaire-5 Items (MEQ-5), which was extracted from the MEQ-19 by Adan and Almiralli through statistical modeling 32. It is proved to have promising psychometric properties, reliability and validity, where the Cronbach’s alpha coefficient for our study was 0.703. Due to the limited number of individuals within the lowest or highest chronotype score group, the chronotype of subjects were divided into evening chronotype (4-11 score), neutral chronotype (12-17 score), and morning chronotype (18-25 score) in current study based on the MEQ-5 score.
Depressive symptoms assessment
The participants were also asked to report their psychological status over the past week through the Patient Health Questionnaire-9 (PHQ-9). It is a simple and effective self-rating scale for the depressive disorder based on the diagnostic criteria of the American Psychological Association 33, which has been demonstrated to have good reliability and validity by previous studies 34, with Cronbach’s alpha coefficient being 0.910 in the present study. It contains 9 items with an overall score ranging from 0 to 27, higher scores indicate more severe depressive symptoms. In the present study, the total score was divided into a dichotomous variable, score >4 points indicate mild and above depressive symptoms, and conversely no depressive symptoms.