Minimal Effect of Daytime Napping Behavior on Nocturnal Sleep in Pregnant Women

Abstract

Study objectives: To assess whether daytime naps negatively impact nocturnal sleep.

Design: Longitudinal, prospective cohort design.

Participants: 161 pregnant women recruited and evaluated in early gestation (10-20 weeks).

Measurements and results: Daily sleep information was collected in three 2-week periods (10-12, 14-16, and 18-20 weeks gestation) with a daily sleep diary and an actigraph. The average number of naps, as well as the average length of each nap, were calculated from sleep diaries. Women were categorized first as non nappers (0 naps/2-week period), moderate nappers (1-3 naps/2-week period), or frequent nappers (≥ 4 naps/2-week period). Then, based on the average nap length, they were categorized as short (< 90 min) or long (≥ 90 min) nappers. Nocturnal sleep parameters included SOL, WASO, SE, and TST. SAS procedure MIXED was used for modeling the main effects of nap group and time, and time by nap group interactions. Women who took naps had a decrease in diary-assessed nocturnal TST, but not actigraphy-assessed TST. This observation was group- and time-specific. There were no other group differences. Women who napped ≥ 90 min had poorer diary-assessed SE and lower diary-assessed TST than those who took shorter naps. Length of nap was not associated with any other sleep measures.

Conclusions: The number of daytime naps have minimal impact on nocturnal sleep parameters; however, long nappers did exhibit modestly impaired sleep continuity and sleep quality. Overall, we propose that daytime naps provide a beneficial countermeasure to the sleep disruption commonly reported by pregnant women. This may be clinically beneficial given that sleep continuity and quality are important correlates of pregnancy outcomes.

Commentary: A commentary on this article appears in this issue on page 593.

Keywords: frequency; naps; pregnancy; sleep; women.

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).

Figure 2. Diary-assessed total sleep time by nap length group and time.

After adjusting for relevant covariates (age, race, marital status, children, exercise habits, caffeine use, BMI, depression, and stress), we observed that long nappers (≥ 90 min) had significantly shorter total sleep time (TST) than short nappers (< 90 min) with a modest group × time interaction (p = 0.062).

Figure 3. Diary-assessed sleep efficiency by nap length group and time.

After adjusting for relevant covariates (age, race, marital status, children, exercise habits, caffeine use, BMI, depression, and stress), we observed a modest difference in diary-assessed sleep efficiency (SE) between the women who took longer naps (≥ 90 min) and those who took shorter naps (< 90 min) at 10–12 weeks (t = 1.89, p = 0.059), and a significant difference at 14–16 weeks (t = 2.52, p = 0.012). The groups were similar at 18–20 weeks.