Sleep, and particularly sleep timing, prior to conception may be important for reproductive and pregnancy health. Evidence of a biological mechanism relating sleep to reproductive health from laboratory studies suggests that sleep may influence the hypothalamic-pituitary-ovarian (HPO) axis. The role of sleep in the HPO axis may also impact many reproductive outcomes including reproductive hormones, ovulation, pregnancy, live birth, pregnancy loss, and adverse pregnancy outcomes. However, epidemiological evidence for associations between sleep, especially sleep timing, and these reproductive health endpoints is limited with most studies typically assessing shift work, and not sleep patterns directly. To address these gaps, we evaluated preconception sleep in association with reproductive hormone panels, anovulation, time-to-pregnancy, live birth, pregnancy loss, and adverse pregnancy outcomes. We used data from 1,228 reproductive aged women with 1-2 prior pregnancy losses in the Effects of Aspirin in Gestation and Reproduction (EAGeR) preconception cohort. Preconception sleep duration, timing, and shift work were measured at baseline via self-report. Reproductive outcomes were assessed prospectively over follow-up. We found weak associations between measures of sleep duration, timing, and shift work with reproductive hormones, but only later sleep timing and shift work were associated with greater risk of anovulation. Longer sleep duration, and later sleep timing were associated with longer time-to-pregnancy, but preconception sleep characteristics were not associated with live birth. Preconception sleep was not associated with risk of pregnancy loss, but later sleep timing was associated with risk of adverse pregnancy outcomes. Together, our findings identify sleep during the preconception period as a potentially modifiable risk factor to improve women’s reproductive health and time-to-pregnancy, and to reduce adverse pregnancy outcomes. Our findings may provide preliminary evidence to suggest that preconception sleep is not associated with pregnancy loss or live birth.