Participants and protocol
The participants were pregnant women who were undergoing pregnancy-related medical examinations at an obstetric medical facility in Nagasaki Prefecture from December 2017 until October 2018. Women who had pregnancy complications were excluded. A total of 143 pregnant women were asked to participate in the study and 113 women consented to participate in this research at their second trimester of pregnancy (around 24 weeks gestation). After accounting for women who dropped out due to obstetric or experienced technological issues related to data collection during the study period, effective responses were obtained from 107 women (74.8%) in the second trimester and 88 (61.5%) in the third trimester (around 37 weeks gestation). The final analysis was performed among 88 participants (Figure 1).
Participants were aged between 19 and 42 years old, with a mean age (± SD) of 30.9 ± 4.7 years. Forty women were primipara (46%). The data were collected at 24.6 ± 0.6 weeks gestation in the second trimester and 36.2 ± 0.9 weeks gestation in the third trimester. The median (interquartile range [IQR]) pre-pregnancy BMI was 20.3 (18.9–22.1) kg/m2 and 6 women (6.9%) were obese (BMI ≥ 25 kg/m2).
All procedures performed this study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This study was approved by the Ethics Committee of Nagasaki University Graduate School of Biomedical Sciences (Approval No. 1711090). Informed consent was obtained from all individual participants included in the study.
We obtained demographic and clinical characteristics of all participants including age, body weight (pre-pregnancy, second trimester, and third trimester), height, history of gravidity, history of parity. Pre-pregnancy, second trimester, and third trimester BMIs were calculated. The delivery and neonatal information were collected from midwifery records including gestational age, duration of birth, type of birth (vaginal delivery, cesarean section), labor induction, episiotomy, perineal laceration, uterus contraction, oxytocic agent use, volume of blood loss, the infant’s condition, infant weight, infant height, Apgar score, umbilical pH, and umbilical partial pressure of carbon dioxide. Self-reported questionnaires related to sleep/wake problems were administered and SDB screening was performed over 2 consecutive nights using a pulse oximeter during the second and third trimester.
SDB was screened using a pulse oximeter (PULSOX-300i, KONICA MINOLTA Japan, Inc., Tokyo, Japan). The pulse oximeter was attached to the first joint of the second or third fingers on the non-dominant hand at bedtime and removed at the time of awakening over 2 consecutive nights. The data were downloaded to a personal computer using DS-Me version 2.1 (KONICA MINOLTA Japan, Inc.). After removing poor measurement periods, the 3% ODI was calculated, defined as the number of times per hour in which the oxygen saturation decreased by 3% or more from the baseline. Patients who had a 3% ODI ≥ 5 were defined as having suspected SDB .
Pittsburgh Sleep Quality Index
Subjective sleep quality was assessed using the Japanese version of the Pittsburgh Sleep Quality Index (PSQI). This questionnaire consists of 7 components including sleep quality, sleep latency, sleep duration, sleep efficiency, sleep disturbance, hypnotic use, and daytime dysfunction. The score of each component ranges from 0 to 3, with global scores ranging from 0 to 21. Higher scores indicate inadequate sleep quality with scores ≥ 6 indicating poor sleep quality [16,17]. ; therefore, women with global scores ≥ 6 were categorized into a “poor sleeper” group. According to a meta-analysis, the sensitivity and specificity (95% CI) for insomnia are 0.94 (0.86–0.98) and 0.76 (0.64–0.85), respectively .
Insomnia Severity Index
Insomnia severity was assessed using the Japanese version of the Insomnia Severity Index (ISI). The severity of difficulty initiating sleep (DIS) and difficulty maintaining sleep (DMS) are answered as “none”, “mild”, “moderate”, “severe”, or “very severe”. Responders who had “mild” to “very severe” symptoms were defined as having DIS and DMS. Responders who had “moderate” to “very severe” symptoms were defined as having moderate to severe DIS and DMS. The global score of this index ranges from 0 to 28, with higher scores indicating greater insomnia severity, and the cut off score for insomnia is 10 points . According to a meta-analysis, the sensitivity and specificity (95% CI) for insomnia is 0.88 (0.79–0.93) and 0.85 (0.68–0.94), respectively .
Epworth Sleepiness Scale
Daytime sleepiness was assessed using the Japanese version of the Epworth Sleepiness Scale (ESS). The global score on this scale ranges from 0 to 24, with higher scores indicating greater subjective daytime sleepiness and the cut off score for EDS is 10 points [20,21]. In this study, we categorized participants with an ESS score ≥ 11 as the EDS group, because a daytime dysfunction score ≥ 2 on the PSQI, which reflects daytime sleepiness, was associated with an ESS score ≥ 11, not an ESS score ≥ 10.
Cambridge-Hopkins Questionnaire Short Form13
Symptoms related to RLS/WED were assessed using the Japanese version of the Cambridge-Hopkins questionnaire short form 13 (CH-RLSq13). The CH-RLSq13 is a self-reported questionnaire containing 13 items, 10 of which are related to characteristic symptoms and the exclusion of other conditions (e.g., leg cramping and positional discomfort); the remaining 3 items are related symptom severity and onset. The sensitivity and specificity of the original CH-RLSq13 for an RLS/WED diagnosis have been reported as 87.2% and 94.4%, respectively, and those of the Japanese version are 88.9% and 100.0%, respectively .
R version 3.5.2 and EZR version 1.40 (http://www.jichi.ac.jp/saitama-sct/SaitamaHP.files/statmed.html)  were used for statistical analysis. Categorical variables were presented as counts and percentages. Continuous variables were presented as the mean and SD when normally distributed and as medians and IQRs when non-normally distributed. Comparisons were made using t-tests for normally distributed data and Mann–Whitney U tests for non-normally distributed data. Comparisons of continuous variables between the second and third trimester were performed using the Wilcoxon signed-rank test. Frequency analyses for categorical data were performed using a Fisher’s exact test. Frequency analyses between the second and third trimester were performed using a McNemar’s test. The 2-sided alpha level was set at 0.05.
The odds ratios for EDS were calculated using logistic regression analysis to assess the association with total sleep time, DMS, and SDB. After a univariate analysis, adjustments for age and BMI were made. Age and BMI were categorized into 2 groups each: age < 30 years (reference) or ≥ 30 years and BMI < 25 kg/m2 (reference) or ≥ 25 kg/m2. Total sleep time obtained from the PSQI was categorized into 2 groups: < 6 hours and ≥ 6 hours (reference). DMS was categorized into 2 groups: none-mild (reference) and moderate-severe. Also, 3% ODI values were categorized into 2 groups: < 5/h (reference) and ≥ 5/h.