Clinical Review
Polysomnographic features of pregnancy: A systematic review

https://doi.org/10.1016/j.smrv.2019.101249Get rights and content

Summary

Symptoms of sleep disturbances are common among pregnant women and generally worsen across gestation. Pregnancy-related sleep disorders are not only associated with a poor quality of life of the affected mothers, but also with adverse perinatal outcomes, including perinatal depression, gestational diabetes, preeclampsia, and preterm birth. The current knowledge about the impact of sleep disorders during pregnancy largely derives from the results of sleep surveys conducted in various populations. However, the number of studies examining changes in objective sleep variables during pregnancy via polysomnography has progressively increased in recent years.

Here we systematically reviewed the polysomnographic studies available in the literature with the aim to describe the sleep pattern and to identify possible markers of sleep disruption in pregnant women.

Based on our analysis, subjective worsening of sleep quality across gestation is related to objective changes in sleep macrostructure, which become particularly evident in the third trimester. Pregnancy per se does not represent an independent risk factor for developing major polysomnography-assessed sleep disorders in otherwise healthy women. However, in women presenting predisposing factors, such as obesity or hypertension, physiological changes occurring during pregnancy may contribute to the onset of pathological conditions, especially sleep-disordered breathing, which must be carefully considered.

Introduction

Pregnancy is a physiological condition of relatively short duration in a woman's life, but characterized by profound biological changes, which have a significant influence on sleep [1].

The typically increased secretion of several hormones across pregnancy considerably impacts on both the circadian and homeostatic components of sleep regulation, leading to modifications of sleep architecture [2]. In human studies, non-rapid eye movement sleep (NREM) has been shown to be enhanced by progesterone and prolactin [3,4], while rapid eye movement sleep (REM) is decreased by progesterone and increased by estrogens [5,6]. Oxytocin peaks during the night, promoting uterine contractions leading to sleep fragmentation [2]. Cortisol and growth hormone levels are also elevated, affecting sleep quality and inducing daytime sleepiness [2].

Besides hormones, other factors contribute to sleep disruption during pregnancy: gastroesophageal reflux, affecting up to 75% of pregnant women [7]; nocturnal micturition, due to an increase in overnight sodium excretion [8]; anatomical changes related to the growing uterus and increased body weight [9]. Moreover, iron and folate deficiency may play a role in the occurrence of sleep-related movement disorders in pregnant women [10,11].

Subjectively reported sleep disturbances are very common during pregnancy, with increasing rates from the first (13%), to the second (19%), and third (66%) trimester of gestation [12,13]. A recent meta-analysis showed that 46% of women experience poor sleep quality during pregnancy, with an average score of the Pittsburgh Sleep Quality Index (PSQI) of 6.4 (95% CI, 5.3–6.85) and with a worsening trend from the 2nd to the 3rd trimester by an average of 1.68 points (95% CI, 0.42–2.94) [14]. While at early gestational age women mainly attribute sleep problems to nausea/vomiting, urinary frequency, and backpain [15], in late gestation up to 69.9% of women report difficulty in maintaining sleep, 34.8% early morning awakenings, and 23.7% difficulty falling asleep [16], mainly due to fetal movements, heartburn, cramps or tingling in the legs, and shortness of breath [13,[17], [18], [19]]. By the end of pregnancy almost all women suffer from recurrent and long wake episodes during the night [17,20].

Self-reported sleep duration also declines across pregnancy [21]. Moreover, objectively assessed sleep duration and quality are related to age and ethnicity, with non-Hispanic black and Asian women having the shortest sleep duration, and younger pregnant women having the highest amount of wake after sleep onset (WASO), the lowest sleep efficiency (SE), and the latest sleep midpoint [22].

To date, the available literature on sleep during pregnancy is mostly based on subjective information from screening questionnaires or interviews [14,19]. However, in recent years, an increasing number of studies investigated sleep in pregnant women objectively, by using polysomnography (PSG) or actigraphy. Sleep parameters derived from actigraphy may significantly differ from those obtained by PSG recordings and should therefore be interpreted with caution [23]. Thus, PSG remains the gold standard for sleep depiction, being the only reliable tool to precisely describe sleep macro- and microstructure, correctly estimate respiratory and motor events, and permit an accurate identification of pregnancy-related sleep disorders.

We here present the first systematic review of polysomnographic studies conducted in pregnant women, with the aim to provide a detailed overview about the intrinsic, objective features of sleep in normal, healthy pregnancy, as well as in some typical pregnancy-related complications.

Section snippets

Methods

We performed a systematic review of the literature by searching for studies reporting objective sleep parameters obtained by PSG in pregnant women until February 1, 2019. The review process followed the PRISMA statement guidelines [24]. The completed PRISMA checklist can be found in the Supplementary material section (Table S1).

Literature search

A detailed flowchart of the results of the literature search process is presented in Fig. 1. Finally, 40 studies were considered for the qualitative analysis (systematic review). Twenty-four of them were cross-sectional studies (n = 24), ten prospective cohort studies (n = 10), five clinical trials (n = 5), and one case–control study (n = 1). Out of 40 studies, n = 27 included a control group, while n = 13 were not controlled. Regarding the country of origin, most studies were performed in the

Discussion

Changes in sleep structure during pregnancy, as objectively measured by PSG, mainly consist in a reduction of sleep duration (TST), due to an increase of WASO, and in a transition from N3 and REM sleep to more superficial NREM sleep stages (N1, N2) [28,29]. As a result, mean SE is diminished and sleep is perceived as non-restorative across gestation [30].

These findings become particularly evident in the third trimester and are confirmed both by studies comparing pregnant with age-matched

Conflicts of interest

The authors have no conflicts of interest to disclose.

Acknowledgements

This work is supported by a grant of the Swiss National Science Foundation (SNSF 320030_160250/1) and a grant of the Ministero della Salute, Italy (“Perinatal depression: chronobiology, sleep-related risk factor and light therapy”, project code: PE-2011-02348727). The authors would like to thank Dr. Giorgio Treglia, MD, for his expert advice regarding the methodology of systematic reviews and meta-analyses.

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