Associations between daytime napping and parameters of ovarian reserve among women undergoing assisted reproductive technology

Circadian rhythm disturbances are known to impair ovarian reserve through endocrine and molecular pathways. However, the specific impact of daytime napping as a common compensatory sleep behavior remains poorly understood. We included 1250 women from the TREE cohort in Wuhan, China. The duration of daytime napping was collected through questionnaires at recruitment. Antral follicle count (AFC) and ovarian volume (OV) were obtained by transvaginal ultrasound. On day 2–5 of a menstrual cycle, blood samples were collected to determine reproductive hormone concentrations. Multivariate Poisson or linear regression models were performed to estimate the associations between daytime napping duration and ovarian reserve indicators. We also performed stratified analysis by nocturnal sleep duration and subjective sleep quality. A total of 624 women (49.9%) reported regular daytime napping. We found that an hour increase in daytime napping was associated with 2.39% (95% CI: 0.24%, 4.58%) higher total AFC. Compared with women who reported no napping, women who reported ≤ 1 h of daytime napping had significantly lower FSH levels (percent change = –6.77%, 95% CI: −10.53%, −2.84%) and lower testosterone levels (percent change = –15.22%, 95% CI: −26.98%, −1.57%). Daytime napping ≤ 1 h was inversely associated with FSH and testosterone levels (P < 0.05). Notably, these participants exhibited a 43% reduced risk of having FSH ≥ 10 IU/L (adjusted OR = 0.57, 95% CI: 0.38–0.84). While hormone levels generally remained within normal ranges, these findings suggest that moderate napping is linked to a more favorable clinical ovarian reserve profile. Daytime napping was associated with higher AFC only among women who reported short nocturnal sleep duration (P for interaction = 0.01), and associated with higher OV only among women with bad sleep quality (P for interaction = 0.01). Daytime napping was associated with higher AFC, and ≤ 1 h of napping was inversely associated with basal serum FSH and testosterone levels. Prolonged daytime napping duration was associated with better ovarian reserve among women who had short nocturnal sleep time and bad sleep quality. Daytime napping may represent a simple, low-cost lifestyle habit that could potentially benefit ovarian reserve, although further prospective studies are needed to validate this association.