Introduction

Pregnancy-related sleep disturbances arise as pregnancy continues [1]. The change in sleep patterns across the term of pregnancy is an item of interest. During pregnancy, pregnant women suffer from poor sleep quality as well as short sleep time, which leads to an increased risk of gestational diabetes mellitus [2, 3], cesarean delivery [4], postpartum depression [5], and preeclampsia. Furthermore, sleep disorder during pregnancy is associated with poor fetal outcome [1], increased rate of abortion and preterm delivery [6], and postpartum pain [7]. This comorbidity of pregnancy may not disappear even after the pregnancy and can cause long-term suffering.

Not only can the sleep during pregnancy affect the life after pregnancy, but also the sleep and its comorbidities also affect the subsequent fertility [8]. Although South Korea’s total fertility rate fell from 1.05 in 2017 to 0.98 in 2018 [9], there are few studies on the sleep of pregnant women. Pregnant women tend to underestimate their bodies while undergoing pregnancy counseling, and sleep status may vary according to ethnic background and may be affected by comorbidity. Therefore, a multifaceted approach, including basic data recruitment, is required for assessment of quality of sleep (QoS) and life (QoL) of pregnant women in South Korea. In order to provide a fundamental data of pregnant women, normal pregnant women who can represent the community are needed. In addition, it is important to know when to pay particular attention to screening for worsening sleep conditions during pregnancy.

The aims of this study are the following: (1) to provide longitudinal data of the monthly-changing sleep status of primigravidae with no previous illness, and (2) to identify the appropriate moment of screening test for sleep disturbance in South Korea. In order to provide fundamental data of pregnant women, normal pregnant women who can represent the community are needed. Besides, it is known that the quality of sleep worsens during the third trimester [1, 10]; taking it one step further, sleep questionnaires were conducted monthly rather than dividing into three trimesters in this study. This monthly-measured quality of sleep, mood, and life assessment provides a detailed picture of how sleep changes during pregnancy, which may suggest an appropriate time for sleep screening.

Methods

Study design

This is a prospective, multicenter observation study, including a university hospital and two regional public healthcare centers for a longitudinal study of sleep status during pregnancy. This study was approved by the Institutional Review Board of a university hospital (No. 2017-11-074).

Participants

All pregnant women filled out the series of questionnaires once a month. In order to evaluate the “standards” of the pregnant women’s sleep status, only primigravidae were extracted. Subjects who had a miscarriage during the follow-up or had any sleep disorder diagnosed before pregnancy were excluded. Also, the pregnant women were excluded if any of the following is diagnosed before or after pregnancy: hypertension, thyroid disease, diabetes mellitus, heart failure, preeclampsia, malignancy, kidney or liver disease, any condition that needs admission, and neurological or musculoskeletal disorders that may affect activities of daily living. All subjects provided written informed consent before enrolling in this study, in accordance with the Declaration of Helsinki.

The questionnaires

From November 2017 to October 2019, all pregnant women visiting the obstetrics clinic in the university hospital or the regional public healthcare centers were asked to fill out a series of questionnaires, including the Korean version of the Pittsburgh Sleep Quality Index (K-PSQI) [11], Insomnia Severity Index (K-ISI) [12], Epworth Sleepiness Scale (K-ESS) [13], Beck Depression Inventory-II (K-BDI-2) [14], STOP (an acronym for Snoring, Tiredness, Observed apneas, and high blood Pressure), and the Short Form-36 Health Survey (K-SF-36) [15]. The questionnaires were validated in Korean, and the cutoff value may be different from that of the original versions. In addition, all subjects were asked to fill out the demographic information query, including age, height, weight, job, previous illness, current medication, and obstetrical history (gravida and para status).

Statistical analysis

Data analysis was performed using SPSS version 22.0 (Chicago, IL, USA). Variables are presented as means ± SD. Repeated measures ANOVA was used to compare the results of the monthly-repeated sleep questionnaires, considered statistically significant if p < 0.05.

Results

A total of 83 pregnant women met the inclusion criteria. Their mean age was 33.11 ± 3.99. Their body mass index (BMI), K-ISI, K-ESS, and K-PSQI gradually increased, while SF-36 gradually decreased through the pregnancy (Table 1). There was a statistically significant difference of BMI between forth and ninth months (26.65 ± 3.92 vs. 23.12 ± 4.11, p = 0.005), of ISI between fifth and ninth months (6.62 ± 3.59 vs. 9.45 ± 5.68, p < 0.001), of K-ESS between seventh and ninth months (5.27 ± 3.19 vs. 7.22 ± 3.77, p < 0.001), and of K-PSQI between fifth and ninth months (6.81 ± 2.82 vs. 8.88 ± 3.62, p < 0.001). There was no subject with more than 2 in STOP and no significant difference in K-BDI-2 during the whole pregnancy. There was a significant difference in K-SF-36 between the fifth and the seventh months (70.76 ± 18.34 vs. 67.34 ± 15.14, p = 0.009).

Table 1 Results of the questionnaires according to the duration of pregnancy
Full size table

The average K-PSQI score in the second trimester was lower than the K-PSQI cutoff value of 8.5 [3], but the average score in the third trimester was significantly higher. This difference in the K-PSQI score may suggest that QoS generally becomes considerably worse in the third trimester of pregnancy. In the details of K-PSQI, subjective sleep quality and sleep duration get worse after the ninth month comparing with that before fifth month (subjective sleep quality, 1.25 ± 0.48 vs. 1.55 ± 0.60; sleep duration, 0.83 ± 1.08 vs. 1.39 ± 1.09), respectively. Although the daytime dysfunction is worst in the first trimester, it does not affect the overall K-PSQI. The others of the details of K-PSQI tended to worsen as pregnancy continues, but there was no statistical difference. In addition, K-ISI and K-ESS scores were also higher in the third trimester, although they did not reach the cutoff scores of 15.5 for K-ISI and 11 for K-ESS [4, 5]. This means that the score increased as the QoS got worse, although it does not show clinical significance.

Discussion

First of all, the mean age of the pregnant women who participated in this study is 33.11 ± 3.99, which is higher than that of other countries varying from 28.6 to 32.7 [16,17,18]. All pregnant women who participated in this study are primigravidae. This old tendency may affect the result of this study since maternal age is known to affect sleep quality [19]. However, given the recent social phenomena of late marriage and late childbirth in South Korea [20], it is a result of current trends rather than limiting the impact of this study.

The score of K-ISI in the ninth month differs from that in fifth. It implies that insomnia might occur somewhere between the fifth and ninth months of pregnancy. However, they did not reach the cutoff score of 15.5 for K-ISI [12], which means the difference and its impact are subclinical. The same is true for K-ESS, of which the cutoff score is 11. Changes in subjective sleep quality and sleep duration resulted in the difference in K-PSQI between the fifth and ninth months, and may support the concept that QoS becomes significantly worse as the pregnancy continues. Given that the cutoff score of K-PSQI is 8.5 or higher [11], the cutoff level fell within the range of standard deviation after the eighth month of pregnancy, and the mean score of K-PSQI exceeds the cutoff value after the ninth month. That implies that sleep deterioration may rise to the surface from the eighth month, and an average sort of pregnant woman may experience clinically significant sleep deterioration since the ninth month.

Depressive mood in pregnancy has been frequently reported [10, 21]; however, pregnant women in South Korea are not as depressed, and the average score of K-BDI-2 is even not changed during pregnancy. The K-SF-36 mental health (MH) as well as K-SF-36 physical health (PH) continued to worsen during pregnancy, reading a significant level after the ninth month. Consequently, the total score of K-SF-36, which stands for QoL, deteriorates during pregnancy to show a significant difference between the fifth and seventh months. It means that there is a relative deterioration of QoL between second and third trimesters. Interestingly, K-SF-36 MH gets worse, although the overall average score of K-BDI-2 never reached the cutoff value (K-BDI-2 > 18 suggests clinically significant depression). It implies that the poor QoL in late pregnancy occurs independently of depression in South Korea.

Since subjective sleep or mood status can be worse than objective scores in pregnant women [16], further studies with detailed history taking and face-to-face interviews are needed. Nevertheless, it is undeniable that the QoL and QoS of pregnant women become worse in late pregnancy and affect the pregnant outcome. It can also affect fertility rate [8]. Further well-designed research for pregnant women’s sleep status and subsequent pregnancy is needed. The degree of symptoms measured in this study would be underestimated, because this study enrolled “normal” pregnant women and subjects with any new-onset disease during pregnancy were excluded. If the analysis included pregnant women with comorbidities, more prominent changes could have been observed. However, this study is significant to confirm that even a “very normal” pregnant woman in South Korea has a significantly worsened QoS as well as QoL at near term.

To the best knowledge of the authors, this is the first study that evaluated pregnant women’s QoS and QoL in South Korea. As their pregnancy continues, women are complaining more sleep problems, including insomnia, excessive daytime sleepiness, and poor QoS [1]. Pregnant women in South Korea also experience getting-worse symptoms of insomnia and daytime sleepiness which have not been before pregnancy, although subclinical. Besides, QoS becomes clinically significant at full term, and QoL changes significantly between the fifth and seventh months. Therefore, screening for sleep and quality of life may be considered in the early third trimester in South Korea. Given that sleep deterioration can lead to a number of comorbidities, clinicians should pay more attention and take a therapeutic intervention approach (e.g., cognitive behavioral therapy or sleep pill for insomnia, lateral position or continuous positive airway pressure for sleep-disordered breathing), if necessary.