Our study was one of the first to evaluate the associations between sleep disturbances and IOL. Only minor findings emerged: habitual snorers and short sleepers were more likely to have IOL. However, these associations vanished in the adjusted models, indicating that sleep disturbances per se do not have a strong impact.
Previous literature evaluating sleep quality in late pregnancy is quite unanimous that sleep disturbances are frequent.7,11,12,14,15 Using the BNSQ, in our two previous studies, in a pilot study with 78 women11 and a follow-up study with 1858 women12, 15% and 30% women, respectively, reported poor sleep quality in late pregnancy. Another Finnish study evaluating sleep also with BNSQ in 325 women, reported that 30% of late pregnant women had restless sleep.15 Further, according to a meta-analysis including 42 studies and using the Pittsburgh Sleep Quality Index questionnaire for sleep quality evaluation, in perinatal period the prevalence of poor sleep was 45%.26 Futhermore, in a study of 2427 pregnant women using also the Pittburgh Sleep Quality Index questionnaire, 76% of the women experienced poor sleep quality across all months of pregnancy.14
Despite of the previously described deterioration in sleep quality during pregnancy, only one earlier study has assessed the relationship between sleep and IOL. Measuring sleep with a wrist actigraphy, Beebe and Lee (2007)7 enrolled 35 women and found no differences between IOL and SOL groups in sleep duration and nightly wake-time after sleep onset five days before labor. Though, interestingly, therapeutical rest, usually implemented by using pain relief medication in early labor, have been shown to decrease the risk of getting IOL.27 Furthermore, maternal tiredness is important indication for IOL; according to the study by Dögl et al (2018)6, about one third of elective IOLs were performed because of mothers request, and indication in every fifth of these IOLs was maternal fatigue and tiredness.
In our study, SDB, especially snoring, as well as short sleep were associated with the likelihood of IOL; however, the associations vanished after adjustment. We adjusted models with age and obesity, which are independent risk factors for SDB development,28 and with comorbidities, which may cause IOL .22,29,30 As for sleep duration, Lee et al (2004)18 showed that short sleep, sleep under 6 h, was a risk factor for CS. This association was also shown in a study including only IOL women.31 In addition, short sleep is associated with gestational diabetes,30 which increases the risk of IOL. Overall, although sleep has some associations with IOL, the likelihood of induction seems to be directly associated with factors other than sleep. Nevertheless, taken all these interactions together, sleep may influence as a mediator in labor and in IOL and thus, should not be ignored.
The strengths of our study are the large size of the study population and the use of BNSQ, a widely used sleep questionnaire among pregnant women.11,12 However, BNSQ was filled in after delivery, and thus, the answers could have been influenced by the entire labor process. Furthermore, sleep was assessed only in late pregnancy, and therefore, our results cannot necessarily be extrapolated to women with long-term sleep disturbances. No sleep architecture was measured, which could have given another perspective to sleep quality. The study population was relatively healthy with uncomplicated full-term pregnancies, and therefore, our results cannot be generalized to women with preterm delivery and pregnancy complications.
Sleep disturbances are common, especially in late pregnancy, and therefore, they may interfere with labor. Although in our study sleep disturbances, especially insomnia symptoms, occurred frequently, they were not associated with the likelihood of ending up to IOL. Still, part of the women in our study had IOL because of maternal tiredness, given that sleep disturbances and plausible daytime consequences, like sleepiness and tiredness, cannot totally be ignored in women in labor. As the rates of IOL are increasing, more research for risk factors for IOL are warranted.