In this longitudinal study of more than 2000 women, we found that pain intensity during labor was not associated with postpartum depression or persistent pain eight weeks after delivery. A negative birth experience was, however, associated with a slightly increased risk for postpartum depression. A history of depression and chronic pain before pregnancy were both important predictors of postpartum pain and depression eight weeks after delivery.
Persistent pain after delivery was reported by 28% of the women, with a substantially higher incidence after caesarean delivery (36%) than after vaginal delivery (26%). This incidence rate is higher than what has been found in previous studies. Eisenach et al reported an eight week pain incidence of approximately 10%, with a minor difference between vaginal delivery (10%) and cesarean delivery (9.2%) [30], while Bijl et al. found an incidence rate of any pain to be 22% and significant pain of 14% three months after delivery [31]. Conversely, another study reported of considerably more pain problems after birth; 79% of mothers with a cesarean section experienced pain at the incision during the first two months postpartum, while 48% of mothers with vaginal births experienced a painful perineum [7]. The different incidence rates are most likely attributable to measurement issues. For instance, the studies by Eisenach et al and Bijl et al ask specifically about pain related to the delivery, Declercq asked even more specifically about pain in perineum or at the incision during the last two months, while we asked a more general question about persistent or recurring pain (anywhere) the preceding two weeks. The postpartum pain rate that we observed could thus include pain not related to delivery, and thus produce a higher incidence rate than in some previous studies, yet a lower incidence rate than studies with a wider time frame. Given the multidimensional nature of persistent pain [32], we nevertheless argue that persistent pain postpartum is relevant to study regardless of perceived attributable cause or anatomical location.
Postpartum depression was reported by 12% of the women, with a slightly higher incidence after caesarean delivery (13.8%) than after vaginal delivery (11.8%). These numbers are comparable to previous studies [30, 33-35], and confirm that postpartum depression is a frequently occuring problem among laboring women.
None of our hypothesized associations between pain intensity during labor and postpartum pain and depression were confirmed. This was contrary to our hypotheses, but may be related to methodological issues. The parturients were asked to rate their intra-partum pain and birth experience within 48h after delivery. Recall bias in patient reported pain intensity is documented in studies of labor pain [36], and intra-partum pain ratings tend to be higher than the postpartum scores [37]. Moreover, the peak-and-end rule in pain is valid for labor pain [38] and may explain why the women report severe labor pain regardless of analgesic treatment: They remember and report the peak pain intensity. In our study the parturients remembered the labor pain as very intense. Actually, more than 50% of the participants reported pain intensity as 9 or 10 on a NRS 0-10 (see figure 2). The lack of association between pain intensity during labor and persistent pain and postpartum depression may therefore partly be caused by a ceiling effect. Nevertheless, the literature is inconclusive when it comes to these associations; some suggest that there is an association [10] and that better pain management during birth could prevent postpartum depression [9, 11, 39] whilst others do not find any preventive effects of analgesia [12, 13]. The conflicting findings could be related to methodological issues as mentioned, but could also be related to differences in medical procedures in the various clinics. In two of the studies that linked epidural labor analgesia to a decreased risk of postpartum depression, epidural was given upon request [39, 40], implying that it was given at an earlier point in time than in our study where it was provided fairly late. Randomized studies of epidural analgesia are challenging, but not impossible. Two recent studies demonstrate this [41, 42], and could serve as a model for future studies that could include postpartum pain and depression as outcomes as well. Nevertheless, postpartum pain and depression is most likely a result of multiple etiological factors, and the jury is still out on whether labor pain intensity is one of them.
Partly in line with our hypothesis, a more negative birth experience was significantly associated with postpartum depression, but not with persistent pain, eight weeks after delivery. The birth experience represents a synthesis of many components, including labor pain. A review of studies of maternal satisfaction concluded that personal expectations, the amount of support from caregivers, the quality of the caregiver-patient relationship, and involvement in decisions are more important than labor pain [43]. A UK population based study supports the relation between overall birth experience and depression. This is further corroborated by a recent intervention study where mindfulness training, carefully tailored to address fear and pain of childbirth, lead to important maternal health benefits in the women, including prevention of postpartum depressive symptoms [44].
An interesting and somewhat surprising finding in our study was the strong associations between both pain and depression before pregnancy and pain and depression eight weeks after delivery. Although Eisenach et al did not find that previous persistent pain predicted postpartum pain, other studies of postpartum as well as post-surgical pain have demonstrated a consistent association between previous pain conditions and incidence of postpartum or post-surgical pain [18, 45]. The same is true for postpartum depression, where a history of depression is a consistent predictor of postpartum depression [15]. However, the association between a history of depression and postpartum pain, or a history of persistent pain and postpartum depression, has never been reported before as far as we know. While chronic pain and depression has been demonstrated to be closely related in the general pain literature [46], very little is known about this association when it comes to obstetric patients. Besides from adding to our understanding of the complex etiology of both postpartum pain and depression, we believe that our findings could add to the pool of significant risk factors for disabling postpartum health concerns. Providing replications of our findings, these risk factors could be included in a screening procedure to identify pregnant women at risk of developing postpartum pain and depression.
In contrast to other reports, we found a positive correlation between labor epidural and pain eight weeks postpartum. Epidural was administered only to women with severe intra-partum pain. In other words, epidural may be a marker of high pain intensity. This association may be confounded by a common risk for both severe pain during labor and
persistent postpartum pain. Only 26% of the women had epidural, and at a mean cervical dilatation of 6.5 cm. This may be regarded as a low frequency of epidurals, and probably provided at a later point in time than optimal [47]. Epidural rates in general vary a lot between birth clinics, and reflects differences in clinical practice and the delivering women’s expectations. The safety of early epidural is well documented [48], but still many laboring woman are encouraged to delay epidural analgesia. Furthermore, women experiencing perinatal distress are much more likely to use epidural [49]. The use of epidural could thus be a marker of distress as well, which could explain the increased risk of persistent postpartum pain in the current study.
Psychosocial factors have an impact on maternal satisfaction. However, characteristics of the analgesia, including its efficacy and its adverse effects, as well as factors related to the pregnancy, the delivery, and the new-born baby might all affect maternal satisfaction and pain relief during labor [50]. Labor pain experience is a difficult clinical outcome to evaluate; more difficult than pain after caesarean delivery [51], in which the prediction models are far more promising. Delivery of a baby is an unpredictable event and our ability to foresee intra-partum complications is poor. Birth experience will be affected by many of these factors and represents the major summarized outcome measure reported by the laboring woman. Development of pre-labor psychological tests to identify high risk women, and corresponding individualized care, appears to be an important way to move forward in addressing this public health issue of postpartum pain and depression [52].
Limitations:
Even if the analyses in the current study are based on a large number of individuals, missing data limits the conclusions to some degree. We have handled missing data through advanced statistical procedures to reduce bias. As data were missing at random we performed multiple imputations. The results were similar without adjusting for missing, thus increasing the reliability of the interpretation.
Intra-partum pain scores in the sample were skewed to the right as most women rated their pain as NRS 9 or 10. This may have complicated the analyses of association with pain and depression eight weeks later. A dataset with repeated intra-partum pain ratings would be more precise, and desirable, but less likely to obtain in such a large sample. Moreover, the delay in utilization of epidural analgesia may have led to increased pain intensity experienced across the board and may thus have skewed the pain data. Finally, the birth cohort only included Norwegian-speaking women, which limits the generalizability of the results somewhat.