In our sample, comprising of late gestational week pregnancies, both insomnia and sleepiness symptoms were common. As described earlier in this article, we found some specific correlations between insomnia symptoms and poor sleep quality and delivery and newborn outcomes. Higher depressive symptoms and higher anxiety symptoms were also associated with delivery and with the use of oxytocin, the latter being a novel finding. However, the absolute risks related to insomnia and mood symptoms were small and thus their clinical significance remains to be evaluated in further studies. Yet, sleep disturbances and mood symptoms are a major health issue during pregnancy and thus should be considered as risk factors for delivery and newborn health.
Emerging evidence indicates that maternal sleep disturbances, especially poor sleep quality, short sleep duration and sleep disordered breathing may contribute to maternal morbidity and adverse outcomes in pregnancy, such as preterm delivery. In a study of 166 mothers by Okun and colleagues  poor sleep quality especially in early pregnancy (14–16 weeks), but also with a tendency in late pregnancy, was a predictor of preterm birth. We found that higher insomnia symptoms were associated with delivery in lower gestational weeks, even though our sample was recruited relatively late in the third trimester. Therefore, in our study, the absolute risk related to insomnia seemed to be lower than the risks reported earlier while the effect of insomnia symptoms already starting in early pregnancy and especially those lasting throughout pregnancy remains unanswered. Thus, more studies are needed, particularly using follow-up samples starting from early pregnancy. We found that higher sleep duration and sleep need were associated with slightly longer duration of pregnancy and this finding supports the thought of better sleep leading to a better pregnancy outcome. Of note is that sleep loss, calculated by subtracting sleep need from sleep duration, was not associated with any delivery or new-born variables.
Prior research concerning antenatal sleep quality and duration of delivery is limited and controversial. Insomnia symptoms and short duration of sleep, especially during the last trimester, have been suggested to predispose to a longer duration of delivery [12, 13] and a higher risk of operative deliveries [11, 12, 31]. In an Iranian study of 457 primiparas in gwk 37 , short sleep duration was associated with a longer duration of all the phases of delivery, whereas worse sleep quality only with a longer duration of the third phase of delivery. Similar results were gained in another Iranian study with 88 mothers whose sleep quality was assessed three weeks prior to delivery . We found somewhat similar results; higher sleep loss (actual total sleep time subtracted from desired sleep need) was associated with longer first phase and total time of the delivery. On the other hand, in our study, neither sleep disturbances nor total sleep duration were associated with the length of delivery. This is consistent with a Canadian study with 624 mothers , and in an American study with 99 mothers  which found no effect of sleep loss on the duration of delivery. One explanation for inconsistencies in results could be the various definitions in the duration of delivery and differences treatment protocols between the countries.
Concerning the mode of the delivery, in the group of 131 American mothers , sleeping less than six hours per night one week before delivery was a risk factor for an unplanned caesarean section. Moreover, the two above described Iranian studies [12, 13] found that both low sleep quality and short sleep duration in the third trimester were risk factors for caesarean section. In a large Swedish study , 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 , 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 caesarean section, neither elective nor acute, which is in line with the results of two earlier mentioned Canadian and American studies [15, 16]. 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 rarely.
Snoring becomes more common during pregnancy probably due to increased weight, oedema, and nasal congestion . Habitual snoring is a known marker for sleep disordered breathing and it can affect maternal and new-born health by raising the risk of pre-eclampsia [8, 10], gestational diabetes  and low birth weight [10, 34]. According to our results, snoring was associated with delivery duration, however, in contrast to our expectations, it was associated with a shorter delivery duration, even though we controlled for maternal BMI, smoking, parity and weight of the newborn. The reason for this finding is unclear and its meaning remains uncertain. Nevertheless, snoring did not relate to other delivery or new-born outcomes. In a large American study of 1673 mothers, snoring during pregnancy was associated not only with a lower new-born birth weight but also with a higher risk of an elective and emergency caesarean section . In another study , however, no association between snoring and delivery was found. Comparing previous studies is challenging, as the methodology varies between the studies.
Prior studies concerning sleepiness and tiredness during pregnancy and their relation to delivery are sparse. In an American study of 1000 mothers, the mean ESS score was higher only among women delivering via elective caesarean section . In a Taiwanese study of 633 low risk mothers, higher fatigue scores predicted caesarean deliveries . In our study, sleepiness or tiredness did not correlate with delivery or neonatal outcomes.
Mood symptoms prior to delivery have been reported to increase the risk of emergency caesarean section . We confirmed 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. In Finland fear of childbirth is one of the leading indications for an elective caesarean section. Mood symptoms anxiety and depression co-exist often with the fear of child birth , and willingness to undergo a caesarean section among these mothers is common. However, probably because of the low number of emergency caesarean in our study, that association was not found. Furthermore, 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 6.6% in 2018 (thl.fi).
High insomnia, 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 . It also plays an important role in increasing maternal-foetal trust and bonding and modulates fear, stress and anxiety . 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 . 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 . 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. However, 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-foetal bonding and presumably is lower in mothers with anxiety, more research is needed to better understand the possible associations.
There are few studies addressing the relationship between maternal sleep and mood symptoms and neonatal outcomes, and most of these studies concentrate on maternal sleep duration. Sleep loss has been shown to negatively affect fetal growth and lead to a lower birth weight . We found that higher insomnia scores and lower general sleep quality was 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 of these associations vanished. These findings emphasized the importance to control for gestational length when studying birth weight. It has also been hypothesised that as a consequence of the suboptimal prenatal environment, the foetus has less resources at birth, resulting in lower Apgar scores . 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 neonates with lower Apgar scores compared to mothers sleeping longer . Nonetheless, in that study, the clinical relevance of the finding remained unclear, since the Apgar scores of the new-born of short sleeping mothers fell 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 neonatal outcomes were found [16, 31]. 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 new-born data drawn from registers. Based on validation studies, the accountability and coverage of the Finnish health care register data are high and reliable . We used BNSQ and ESS questionnaires, which have been shown to be valid and reliable and have been used in similar studies earlier. However, there were limitations to the study. In our cohort, the caesarean and vacuum assisted delivery rates were 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. Nevertheless, the report errors were probably randomly distributed and thus equivalent for all of 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.