In our sample, comprising of late gestational week pregnancies, both insomnia and sleepiness symptoms were very common. As described earlier in this article, we found some specific correlations between sleep disturbances and delivery and newborn outcomes. However, the absolute risks related to insomnia and mood symptoms were small and thus their clinical significance remains unclear.
As stated earlier in this article; maternal poor sleep during pregnancy is a risk factor for preterm delivery [9, 10]. We could not confirm this finding of prematurity, but still in our study insomnia symptoms were associated with delivery in earlier gestational weeks, albeit the effect was low. We also found that longer sleep duration and higher sleep need were associated with slightly longer duration of pregnancy. This finding supports the thought of sufficient sleep leading to a better pregnancy outcome. Of note was, however, that sleep loss, calculated by subtracting sleep need from sleep duration, was not associated with any delivery or newborn variables.
Our sample was recruited relatively late in the third trimester and thus the actual insomnia symptoms may have been short time, which could explain our weaker findings. In addition, the women delivering very preterm were presumably less likely to participate in the study as the recruitment of the participants started around 30th week of pregnancy. Thus, more studies are warranted, particularly using follow-up samples starting already from early pregnancy.
Prior research concerning maternal sleep disturbances and duration and type of delivery is limited and partly controversial. Insomnia symptoms and short sleep duration, especially during the last trimester, have been suggested to predispose to a longer duration of delivery [13, 16]. We found partly similar results; sleep loss was associated with longer first phase and total time of the delivery. On the other hand, in our study, neither sleep disturbances, sleep quality or total sleep duration were associated with the duration of delivery. This is consistent with an American study with 99 mothers [18] which found no effect of sleep quality or sleep duration on the duration of delivery phases. One explanation for inconsistencies in results could be the varying clinical practices between the countries and the differences in the ways of notating the delivery durations.
Concerning the mode of the delivery, in the group of 131 American mothers [14], sleeping less than six hours per night one week before delivery was a risk factor for unplanned caesarean section. Moreover, the two earlier described Iranian studies [13, 16] found that both low sleep quality and short sleep duration in the third trimester were risk factors for caesarean section in general. In a large Swedish study [34], the researches screened retrospectively the electronic perinatal records of 6467 primiparas for free-text words that indicated stress, sleep disturbances and worry, and found that the existence of these words in the charts predicted an increased risk for an emergency caesarean section. In addition, in a Taiwanese study of 120 mothers [35], poor sleepers in the third-trimester were more likely to have a vacuum-assisted delivery. We could not confirm the associations between sleep disturbances and the mode of delivery. We found no correlation between maternal sleep and caesarean section, neither elective nor acute, which is in line with the results of the earlier mentioned American study [18] and also with a Canadian study of 624 women [17]. Of note is, that assessment of sleep disturbances in previous studies has varied widely and structured sleep questionnaires, as used in our study, have been utilized seldom. Furthermore, the frequencies of instrumental deliveries, and especially the rates of caesarean section ranges considerably between the studies (and countries) from our 10 % to even 55 % [15–17].
According to our results, snoring was associated with delivery duration, however, in contrast to our expectations, it was associated with a shorter delivery duration. The reason for this finding is unclear and its meaning remains uncertain. Earlier, in a large American study of 1673 mothers, snoring during pregnancy was associated not only with a lower birth weight but also with a higher risk of an elective and emergency caesarean section [8]. In another study [36], however, no association between snoring and delivery was found. Nevertheless, in our study, snoring did not relate to other delivery or newborn outcomes so this finding could also be a random association. Comparing previous studies is challenging, as the methodology varies between the studies.
Depressive symptoms prior to delivery have been reported to increase the risk of emergency caesarean section [25]. We found only that severe mood symptoms, both depressive and anxiety symptoms, were associated with elective caesarean section: mothers with higher depressive score had an almost five times and mothers with higher anxiety scores an over two times higher incidence. No association with emergency caesarean emerged. Our finding of the risk for elective caesarean is probably explained by fear of childbirth. Mood symptoms, anxiety and depression, co-exist often with the fear of child birth [37], and willingness to undergo a caesarean section among these mothers is common and today fear of giving birth is the leading cause for elective cesarean in Finland. The importance of our finding was notable, especially since the caesarean section rate in our study was low as the sample was recruited at the third trimester and breech and twin pregnancies were excluded. The overall elective caesarean section rate in Finland was 7,0% in 2019 (thl.fi).
High insomnia score, high depressive score and high anxiety score correlated with the use of oxytocin during delivery. These findings were novel ones. Oxytocin causes the contractions of the uterus during delivery and stimulates lactation [38]. It also plays an important role in increasing maternal-fetal trust and bonding and modulates fear, stress and anxiety [39]. Anxiety which occurs in the third trimester and during delivery has been shown to have negative effects on the duration of all the phases of delivery [40]. In addition, in a recent large retrospective study women exposed to additional oxytocin during delivery were at a higher risk for the development of postpartum depressive and anxiety disorders [41]. Mood symptoms often co-exist with insomnia, so the finding of all these symptoms leading to the need of oxytocin is rational. It is possible that pregnant women suffering from insomnia or mood symptoms have lower levels of oxytocin during delivery or they have a decreased binding ability of oxytocin to the uterine oxytocin receptors and therefore these women need additional oxytocin stimulus. Unfortunately, in our cohort we could not reliably find out whether the oxytocin used during deliveries was for induction or for augmentation. In addition, the use of oxytocin during delivery is also dependent on the physician and mid-wife policy and can vary widely. As oxytocin is important in maternal-fetal bonding and presumably is lower in mothers with anxiety, more research is needed to better understand the possible associations.
There are only few studies addressing the relationship between maternal sleep and mood symptoms and newborn outcomes, but most of these studies concentrate on maternal sleep duration. Sleep loss has shown to negatively relate to fetal growth and lead to a lower birth weight [19]. We found that higher insomnia scores and lower general sleep quality were associated with lower birth weight and longer sleep duration and longer sleep need with slightly higher birth weight. Nevertheless, when the birth weight was standardized with gestational age at delivery, all these associations disappeared. This emphasizes the importance to control for gestational length when studying birth weight. It has also been hypothesized that as a consequence of the suboptimal prenatal environment, the fetus has less resources at birth, resulting in lower Apgar scores [12]. Again, according to the Iranian study with 457 participants, mothers sleeping less than eight hours per day in the third trimester have shown to deliver newborns with lower Apgar scores compared to mothers sleeping longer [13]. Nonetheless, in that study, the clinical relevance of the finding remained unclear, since the Apgar scores of the newborn of short sleeping mothers fell also within the normal range. In our study, no clinically relevant correlations emerged. This was true also in a Chinese study with 248 women and in a Canadian study with 650 mothers, where no correlations between maternal sleep variables and newborn health state at delivery were found [17, 35]. However, of note is, that our study did not consider the effect in the case of very preterm newborns.
Our study comprised of a large sample of pregnant Finnish women recruited during the third trimester and delivery and newborn data drawn from registers. Based on validation studies, the accountability and coverage of the Finnish health care register data are high and reliable [42]. We used questionnaires, which have been shown to be valid and reliable [31] and have been used in similar studies earlier [43]. However, there were limitations to the study. In our cohort, the caesarean and vacuum assisted delivery rates were significantly lower than in the general population in Finland and therefore there might be a selection bias in the results. Concerning the caesarean, the main reason for the low rate was the exclusion of breech presentation, twin pregnancies, and very preterm deliveries. The study assessed maternal sleep over the past months before delivery and can therefore reliably present only the effect of sleep in late pregnancy. The study was based on subjective questionnaires and no objective sleep data was collected. It is known that objective measurements of sleep can differ considerably from subjective self-reported sleep [44]. Nevertheless, the report errors were randomly distributed and thus equivalent for all the participants. In addition, our cohort comprised of women delivering mainly full term and thus our study did not consider the effects in the case of very preterm newborns, so the results cannot be interpreted in preterm cases.