Figure 1. Average minutes of diary-assessed total sleep time by nap group and time.

After adjusting for relevant covariates (age, race, marital status, children, exercise habits, caffeine use, BMI, depression, and stress), we observed a main effect for nap group on subjective total sleep time (TST), but no group × time interaction. At 10–12 weeks, women who napped with moderate regularity (1–3 naps/2-week period) had more self-reported total sleep time compared to frequent nappers (≥ 4 naps/2-week period) [t = 3.00, p = 0.0088]. There were no differences among the groups at 14–16 weeks. However, at 18–20 weeks, women who did not nap had more self-reported total sleep time than frequent nappers (t = 2.83, p = 0.015). Prior to adjustment there was a modest difference between the moderate and frequent nappers in TST (t = 1.80, p = 0.072), but after adjustment, the moderate nappers were similar in TST to frequent nappers (p = 0.201).