Background
Insomnia is one the most common health complaints in the general population, and is associated with substantial individual [
1] and societal consequences [
2]. With rising prevalence rates over the last decade [
3], it is now estimated that approximately 10–15 % of the adult population fulfills the diagnostic criteria for insomnia disorder [
3]. Women experience more insomnia than men [
4], a gender pattern which emerges in late adolescence [
5]. Pregnancy and the postnatal period may be an especially vulnerable period for the development of insomnia and other sleep disturbances in women. This is not surprising given the many physical and physiologic changes during pregnancy. Similarly, nighttime feeding and the frequent nocturnal awakenings among infants are important factors for understanding sleep deficits and reduced sleep quality among mothers in the postnatal period [
6].
Short sleep duration and symptoms of insomnia may thus be regarded as common phenomena during pregnancy and the postnatal period. Previous findings show that the first trimester is typically characterized by an increase in total sleep time and daytime sleepiness [
7], whereas the majority of pregnant women experience reduced sleep quality and more nocturnal awakenings later in pregnancy [
8‐
13], and immediately after birth [
14‐
16]. However, these findings are primarily based on small-scale studies, and there is still a lack of population-based studies assessing the quantity and quality of the sleep of women during pregnancy and postpartum. Furthermore, to the best of our knowledge, no studies have investigated whether such sleep problems continue beyond the first few months postpartum. A longitudinal population-based study from Norway recently showed that nocturnal awakenings become less frequent when toddlers reach 18 months of age [
6], suggesting that also the mothers sleep may improve at this stage compared to the weeks and months immediately after the birth. On the other hand, insomnia often takes a chronic course [
17], and it has yet to be investigated whether sleep problems emerging during pregnancy continue beyond the infant stage and into toddlerhood.
Moreover, previous findings from the same data that is used in the current study have shown that depressive symptoms and sleep problems are closely interrelated, both in late pregnancy (week 32) and in the postnatal period (8 weeks postpartum) [
18‐
20]. Therefore, to better understand the extent to which sleep problems endure over time in this population, depressive symptoms need to be accounted for when examining the chronicity of sleep problems from the pre- to postnatal period.
Based on the above considerations, the aims of the current study were 1) to describe the natural development and stability of insomnia and short sleep duration from pregnancy to 8 weeks and 2 years postpartum, and 2) to examine to what extent the predictive effect of early sleep problems during pregnancy on maternal insomnia in toddlerhood may be explained by postnatal depressive symptoms.
Discussion
In short, we found an overall pattern indicating stable or increase in sleep problems from pregnancy to immediately after birth (8 weeks). Whereas the mothers reported relatively fewer sleep problems 2 years postpartum compared to the first two time periods, there was a high stability of insomnia over the three assessment points. Sociodemographical and clinical factors, including concurrent maternal depression could not explain the stability of sleep problems during and immediately after pregnancy, to sleep problems 2 years postpartum.
Sleep duration decreased from pregnancy to the postnatal period from 7 h and 16 min to 6 h and 31 min in the current study. This is in line with a pattern of reduced sleep duration reported by the Hedman study [
8]. A similar conclusion was reached by Lee et al. [
7] who also found that sleep disturbances were greatest during the first postpartum months. The reduced sleep duration is not surprising given the care demanded by the baby at this time point, including nighttime feeding and the often erratic sleep patterns in newborn babies. Extending these findings, the current study found that the sleep duration had significantly increased to 6 h and 52 min when the child was 2 years old, which is closer to, but still less than the previously reported average sleep duration among Norwegian women aged 40–44 (7 h and 11 mins). A similar pattern was observed for both SOL and WASO. Insomnia showed a high level of chronicity in the present study. While insomnia symptoms increased during the early postpartum period, and declined by 2 years postpartum, the prevalence of insomnia remained very high at year 2 postpartum. Forty-one percent of the women still fulfilled the DSM-IV criteria for an insomnia diagnosis according to the BIS, which is substantially higher than prevalence estimates among women in the same age group (12–17 %) in the general population in Norway [
3]. However, when comparing our findings with the validation study of the BIS [
21], which included data from women in reproductive age, the differences in insomnia symptoms were smaller. The women in our study reported more nights with non-restorative sleep, and more days with sleep dissatisfaction, while there were only small or no differences on the other BIS items.
Previous studies in the general population have found large age-gender differences when estimating the prevalence of insomnia. For example, whereas a large Norwegian population-based study found few gender differences in young adults, the insomnia prevalence seems to increase markedly from 35 years of age, especially in women, and only to a lesser extent in men [
4]. Although few studies have investigated the mechanisms driving such gender differences, it is possible that sleep problems developed during pregnancy may become chronic, and as such contribute to explaining why middle-aged and older women suffer from more sleep disturbances. Future longitudinal studies that track sleep beyond the early years postpartum are needed to explore this hypothesis further. There are, however, other factors which are also likely to explain this gender effect, such has hormonal changes following menopause [
29] and gender differences in shift-work occupations [
30].
A previous study based on the same dataset as the current study found a close association between insomnia and depression [
18], emphasizing the importance of taking depressive symptoms into account when assessing sleep problems in this group of women. However, adjusting for maternal depression did not attenuate the predictive effect of previous maternal sleep problems on neither insomnia status nor short sleep duration at 2 years postpartum. This suggests that the development of chronic sleep problems in this cohort may be largely independent of comorbid postnatal depressive symptoms, despite these conditions being closely interrelated.
The results confirm a rapidly changing pattern of sleep during pregnancy and the first years. Knowledge about the normative sleep pattern among mothers may be important to communicate both realistic expectations in this period, as well as discussing preventive efforts to improve sleep among pregnant women and during early motherhood. Short sleep duration and insomnia are related to a range of impaired functional outcomes, and thus the alterations in sleep may impact the daily life for these women and their children. While some sleep alterations are normative and may be expected, it may be important to prevent chronic sleep problems among new mothers through preventive programs. For some women, the insomnia and sleep problems may be at a level that needs intervention and clinical attention. While treatment for insomnia is efficacious in the general population, tailored interventions may be needed to specifically target pregnant and postpartum women.
The results from the current study must be interpreted in light of several methodological limitations. First, all sleep data were based on self-reported instruments, and not a clinical evaluation or objective measures. Also, while some important confounders were controlled for, other variables that could have influenced the association, such as other maternal psychopathology or medical conditions, were left unexplored. Moreover, the first assessment point in the current study was during pregnancy, and as such, we do not know how many of the woman had suffered from sleep problems or insomnia before they were pregnant. Also, the response rate across all 3 time points was not high, which may limit the generalizability of the sample. Unfortunately, the problem with non-participation in survey research seems to be on the rise [
31]. It should also be noted that there were notable differences between the responders and non-responders, with responders being older, more educated, and more likely to be married/cohabitating. Of note, however, no differences in sleep were observed in women who completed all there waves compared to women who dropped out after T1 or T2.
There are several strengths in the present study. The current study is one of the largest studies of sleep during pregnancy, and, to the best of our knowledge, the only prospective study assessing maternal sleep from pregnancy into toddlerhood. As such, it expands on the findings by Hedman et al. [
8] who followed 325 pregnant women from 3 months before pregnancy to 3 months after delivery. This may limit the generalizability of the findings. Moreover, this study is, to the best of our knowledge, the largest longitudinal study of sleep problems during and after pregnancy. Also, the questionnaires used in the current study are well-validated instruments, and the BIS has been shown to correspond well with objective sleep measures, including polysomnography (PSG) [
21]. And although self-reported sleep parameters, including SOL and WASO typically differ from those obtained from objective assessments [
32], recent studies have shown that such self-report sleep assessments can be recommended for the characterization of sleep parameters in both clinical and population-based research [
33]. Still, the BIS has not been validated for sleep problems in pregnancy. Similarly, although the EPDS does not provide a clinical diagnosis of depression, it is well suited to assess symptoms of depression among Norwegian postpartum women [
24], and the use of the continuous scale (as used in the current study) is also in line with the recommendations for use in population-based research [
34].
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
Author BS and MH drafted the manuscript and conducted the statistical analysis. Author MEG was responsible for conception and design of the study and was involved in acquisition of data. Author SD was involved in the design of the study and SD and MEG gave critical revision of the manuscript for important intellectual content. All authors read and approved the final manuscript.