Study design and subject recruitment
This study was conducted as a prospective observational study at Wayo Women’s University between February 2019 and May 2020. The participant recruitment method involved explaining the research to the physician in charge of the obstetric clinic that performed normal deliveries and obtaining their cooperation in this study. We were introduced to primiparous women with natural pregnancies and no complications from the cooperating institutions, and we provided a verbal explanation to the participants using an explanatory document, after which we obtained written informed consent. The participants were assured that their participation was voluntary and they could withdraw from the study at any time. The participation in the study was discontinued if abnormalities such as threatened premature birth, complications, and the onset of high-risk pregnancy occurred during the pregnancy period.
Inclusion and exclusion criteria
Primiparous women aged 20–40 years who had conceived naturally, who had no complications, whose fetal heartbeat was confirmed by ultrasound, and who were willing to provide informed consent were included in the study. Women who found it difficult to comprehend the Japanese language and were unable to answer the questionnaire in Japanese were excluded from the study. Additionally, women who were judged inappropriate as participants of the study by the principal investigator or the physician of the research cooperation facility were excluded.
Data collection
The data of the participants were collected at three time points, during the first (10–14 weeks), second (16–27 weeks), and third (28–37 weeks) trimesters, of pregnancy. The participants also answered a questionnaire survey, and their 7-day actigraph sleep activity measurements were recorded. They also maintained a sleep diary.
Basic information of the participants, including age, number of weeks of gestation, weight gain during pregnancy, presence or absence of anemia, and working status, was collected using a questionnaire. Participants were also asked to use the visual analog scale (VAS) [10] to rate the severity of minor troubles that occurred during pregnancy, such as presence or absence of anemia, morning sickness, dizziness, constipation, pollakiuria, low back pain, stiff shoulders, back pain, headache, leg cramps, leg varicose veins, hemorrhoids, itchy skin, swelling, heartburn, and leucorrhea.
Subjective assessment of the participants
The Japanese version of the Pittsburgh Sleep Quality Index (PSQI-J) [11] was used to evaluate sleep quality. The Pittsburgh Sleep Quality Index (PSQI) [12] has been widely used in several clinical and epidemiological studies; it consists of seven factors related to sleep quality, viz., sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, daytime dysfunction, and disturbance to daily life; the total score (0–21 points) is calculated by adding the scores of each component (0–3 points), wherein a higher score indicates more disturbed sleep. The cut-off score is 6 points, with 6 or more points indicating poor sleep.
Furthermore, the Medical Outcomes Study Questionnaire Short Form 36 (SF-36) [13, 14] was used to assess health-related quality of life (QOL). SF-36 is a global measurement scale that does not limit measurements to patients with specific diseases. It can be used for both healthy individuals as well as those with diseases, and it is possible to continuously monitor the health conditions. SF-36 has eight subscales, each with a score range of 0–100 points. A higher score indicates better conditions. SF-36 enables the scoring of physical, mental, and social functions as summary scores.
Objective assessment of the participants
A wristwatch-type sleep measurement device (actigraph by Sanita Trading Co. Ltd., Japan) was worn 24 h a day by the participants, and their sleep conditions were measured for 7 days. The actigraph is a device that is specifically designed to analyze the circadian rhythm from the perspective of sleep physiology, and it has been used in many studies, including those involving with sleep medicine [15].
Maintenance of sleep diary
Paticipants used VAS to record time taken to fall asleep and wake up. During the device-wearing period, the participants also recorded their “feeling of being refreshed when waking up in the morning” each morning and their “sense of fatigue for the day” before going to sleep. The scores ranged from 0–100, with a higher score indicating better conditions.
Endpoints
The primary endpoint was sleep efficiency as determined from actigraph measurements. The secondary endpoints included total sleep time as determined from actigraph measurement, subjective sleep using the PSQI-J, feeling of being refreshed when waking up in the morning using VAS, and health-related QOL using SF-36.
Determination of sample size
Considering the feasibility and scale of a previous study [15], the target sample size for this study was set at 40. For the main comparison (comparison of changes in sleep efficiency), the sample size was determined with an effect size (mean difference/standard deviation) of 0.55, a two-sided significance level of 5%, and a power of 90%, which resulted in 35 detectable cases. After considering the dropout cases, the scale of the study was set to 40.
Statistical analyses
Data are presented as means ± standard deviations. Questionnaire-based sleep quality (PSQI score), health-related QOL (SF-36), and actigraph-based sleep activity measurement results (sleep efficiency, number and duration of wake after sleep onset, activity level) were compared using time-series correspondence tests. Repeated measures analysis of variance was used to compare the data for the first, second, and third trimester of pregnancy. Tukey’s honestly significant difference test was used for post-hoc analysis. Pearson’s correlation coefficient was used to identify the correlation between sleep efficiency and minor troubles. All analyses were conducted using the JMP software, version 14 (SAS Institute, Inc., Cary, NC, USA).