Resolution of Pain after Childbirth

Major physical trauma, including surgery, results in nearly universal acute pain which resolves in most individuals over weeks to a few months. For those with pain several weeks after surgery, pain resolves slowly, with an estimated half-life of 6–7 yr.1,2Thus, if the initial incidence is high, the burden on patients and health care can be great. Important risk factors for chronic pain after surgery include the degree of tissue trauma and preexisting patient characteristics, especially preexisting chronic pain.3,4Childbirth is associated with physical trauma and nearly 1/3 of deliveries are performed by cesarean section in the United States. In a 2-yr follow-up of nearly 1,000 women for breech delivery by cesarean section, there was a 20% incidence of pain, mostly comprising back- and headache, with approximately 5% with pain in the superficial or deep abdomen.5A Danish postal survey indicated pain in the surgical area of 19% at 3 months and 12% at 10 months after cesarean delivery, with half of these women experiencing daily or near daily pain.6These data suggest that childbirth, especially cesarean delivery, represents a major cause of chronic pain in women.Previous studies have often not critically separated new pain after the surgery from pre-existing pain. For example, of the 32% of 1,300 Danish women experiencing pain 1 yr following abdominal hysterectomy, only 4.4% ascribed new pain from the surgery itself.4During pregnancy there is a high incidence of abdominal, back, and pelvic pain,7,8which could, if included, inflate the observed incidence of chronic pain from childbirth. To better understand the incidence and risk factors for chronic pain after delivery, we performed a prospective, multicenter study with specific focus on new pain which began at the time of labor and delivery. We previously reported that presence of this pain and postpartum depression 2 months after delivery was predicted by severity of acute, post-delivery pain but not by mode of delivery (vaginal or cesarean).9That report9represented a secondary analysis of the Pain After Delivery study, whose primary outcome measure was the incidence of pain beginning at the time of delivery and still present 1 yr after childbirth. Here we report the results of this primary outcome analysis.A secondary purpose of this study was to generate a predictive model of chronic pain after childbirth. The extremely low incidence of pain 6 and 12 months after delivery did not allow us to generate such a model for truly chronic pain. Nonetheless, approximately 10% of women in this study had persistent pain 2 months after delivery, which interfered with their normal activities,9and a similar proportion suffered from post-partum depression at this time. We therefore sought to generate a predictive model for pain and depression 2 months after delivery, asking whether factors other than the severity of acute post-delivery pain were involved. Because past history of pain10and degree of surgical trauma3have been associated with risk of chronic pain after other types of surgery, we applied a data reduction strategy which focused primarily on these factors.Following Institutional Review Board approval and written informed consent, 2,518 women hospitalized for childbirth at Forsyth Medical Center, Wake Forest University, Winston-Salem, NC, Columbia University Medical Center, New York, NY, Université Catholique de Louvain, Brussels, Belgium, and Hôpitaux Universitaires de Genève, Geneva, Switzerland from September 2004 to December 2005 were interviewed within 36 h of delivery and their medical records reviewed, with focus on characteristics of pregnancy and delivery and past medical history, including history of pain during or preceding pregnancy. Full details of the interview questions and chart review are provided in our previous publication from a secondary analysis from this dataset.9Although all pain was recorded, the primary outcome measure was defined as pain which began at the time of labor and delivery and included a location which could be ascribed to the delivery (pelvis, perineum, abdomen). Patients were then contacted at 2, 6, and 12 months after delivery and questioned regarding these specific locations of pain beginning at the time of labor and delivery using a scripted telephone interview with simultaneous data entry by interviewers (US sites), or postal survey (European sites). Because of the different methodology of follow-up and response rate between the United States and European sites, the European data were not used for long-term follow-up in the current study, nor were they used in the 2-month report.9Patients who reported pain which began at the time of delivery and which was still present 2 months later were contacted by telephone at 6 months, and those with pain at 6 months were contacted again at 12 months after delivery. At both 6 and 12 months, subjects were queried regarding their average and worst pain for the preceding week as well as the intensity of their current pain using a 0–10 verbal scale, with 0 being no pain and 10 being the worst imaginable pain. Patients were asked to describe their pain using the short form McGill Pain Questionnaire,11its location, its effect on various activities of daily living, and whether they sought medical attention for its treatment. For activities of daily living, subjects were asked whether pain affected walking, standing, climbing stairs, getting up from a chair, carrying bags, driving, participation in athletics, or working and whether effects of pain were present on their mood, sleep, or ability to concentrate. In addition, at the 6-month interview, the degree to which their pain was neuropathic in character was quantified using a validated inventory described by Bouhassira et al .12Finally, the presence of depression at the 12-month interview was assayed using the Edinburgh Post Partum Depression Inventory, a series of questions validated for the postpartum period.13There were two goals of data analysis: (1) to describe the incidence of the onset and course of delivery-related pain; and (2) to generate a predictive model for pain and depression at 2 months after delivery.The estimation of pain incidence at each measurement occasion is straightforward without missing data. According to the study design, each participant was queried about the existence of pain related to her delivery at each measurement occasion as previously described.9After a participant indicated that she did not have pain related to her delivery, she was not queried at later occasions and a “no pain” score was imputed for the remaining measurement occasions. The value of this plan is based on the assumption that pain related to delivery is unlikely to remit and then re-initiate at a later time. It is of note that these individuals could not be lost to observation, because no attempts were made to contact them after they reported being pain free. This is in contrast to the individuals who continued to report pain and who were contacted at each measurement occasion. These individuals could be lost to observation, thus potentially biasing the incidence estimate downward. To account for this differential pattern of missing data, three different estimates of the incidence rates were calculated and reported for each measurement occasion.The first estimate of the incidence rates assumed the data were missing completely at random and were simply calculated as the observed proportion of participants with pain at each time point. Because of the specific potential for downward bias induced by the sampling plan, this estimate served as the lower bound of the incidence rate. The second estimate of the incidence rate assumed that the data were missing at random and was calculated using several multiple imputation (MI) models.14,15Multiple imputation assumes that the values for the missing outcomes are conditional on the values of the actually observed outcomes (and other predictors). The MI procedure draws repeated estimates of the missing values to impute plausible values, and these values can be combined to produce estimates of the likely values for these missing data. The MI models were conducted using Proc MI (SAS 9.2; SAS Inc. Cary, NC) with 100 imputations. One model was created for each measurement occasion (2, 6, 12 months) with the presence/absence of pain being conditional on study site, worst pain rating within 72 h after delivery, parturient age, gestational age, total neonate weight, reported pain with menstruation, number of fetuses, previous history of cesarean section, intensive care unit admission during birth, previous delivery problems, smoking status, alcohol use, reported pain during pregnancy, delivery type, reported state of health, and somatization score. The final estimate of pain incidence assumed the data were not missing at random. These estimates relied on the same MI model predictors, but assumed that having pain at the previous measurement occasion increased the probability of being lost to observation on the next occasion (pain drop out model). To produce this effect, the MI models were conducted iteratively, with the results of each measurement occasion informing the next such that the imputed values from the previous measurement occasion were used to impute the next value. These estimates served as the likely upper bound of the estimates.To accomplish the second goal of the analysis, two analytical steps were undertaken. Because pain after delivery was previously demonstrated to be related to the presence of pain at 2 months,9we sought to develop models that predicted pain after delivery to examine whether these predictors could themselves predict prolonged pain. First, a multivariate association between three estimates of the post-delivery pain experience (pain now, worst pain, average pain) was examined with three different theoretical predictor groups (patient characteristics, pain history, and tissue damage) to determine whether any of these predictor sets could predict any element of the pain experience. All of the individual predictors from these three groups are listed in table 1.Canonical correlation was used to examine the multivariate associations.16Canonical correlation examines the association between two sets of variables (rather than two variables as in bivariate correlation) by creating linear composites of each set that maximizes the association between the sets.16There are a number of different solutions that could be applied (with the number of sets being equal to the least number of variables in either set), and each solution weights the variables in a unique way, highlighting different aspects of the multivariable relationships. Each association can be evaluated using a traditional inference, with the strength of the relationship indexed using multiple R 2. In this way, the greatest observable association is created by weighting the variables optimally to produce optimal associations.The second analytical step utilized the canonical variates (i.e ., weighted scores) from the first step to produce total scores for each of the predictor sets. These total scores were used to predict the presence or absence of pain and the degree of depressive symptoms at 2 months. To accomplish this, all three total scores were forced into a logistic regression to predict the presence of pain and a linear regression to predict the severity of depressive symptoms each at 2 months.Unless otherwise stated, data are presented as mean (SD) or median (interquartile range). Nonparametric data in the description of patients with pain at 6 and 12 months were compared using Mann–Whitney U test. All analyses were conducted in SAS 9.2. Where appropriate, all inferences are two-tailed with P value less than 0.05 interpreted for statistical significance. No efforts were made to adjust P values for multiplicity. The interpretation of the multiple R 2should be made with caution because data driven procedures, like canonical correlation, capitalize on chance associations within the data and are thus expected to shrink on replication in future datasets. However, the goal of the present analysis was to examine whether any combination of the predictor sets had value in predicting future pain state in this dataset , making these data driven procedures defensible.From September 2004 to December 2005, 2,518 patients were enrolled at the four study sites. After excluding the European sites because of poor differences in methodology and response rates (n = 1,290), the number of participants available for analysis at the American sites were N = 1,228. Two analysis sets were derived from these available participants, the pain prevalence set that utilized all available participants to estimate the incidence of pain after delivery, and the pain predictor set that utilized only the n = 937 participants that were available at each of the measurement occasions for the creation of incidence models (See fig. 1).The characteristics of these patients have been extensively detailed in the analysis of effect of mode of delivery on pain 2 months later.9Briefly, n = 837 (68.2%) of the participants had a vaginal delivery, whereas n = 391 (31.8%) underwent a cesarean delivery. The mean (SD) age for parturients was 29.2 (6.4) years, with a mean body mass index of 31.6 (6.8). At delivery, the mean gestational age was 38.4 (2.6) weeks, with 1,178 (95.9%) of paturients giving birth to singletons.Figure 2displays the observed incidence of pain along with two estimates of the likely incidence in the population, given that the available sample exhibited missing data. Although 1,169 of 1,223 (95.6%) of participants reported pain immediately after delivery, the observed rate fell to 95 of 972 (9.8%) at 2 months, 17 of 942 (1.8%) at 6 months, and 3 of 937 (0.3%) at 1 yr. Our efforts to consider missing data using several imputation strategies led to slightly higher pain incidence estimates (with likely lower and upper bounds) of 10.0% (9.8–10.1%) at 2 months, 2.8% (1.4–5.3%) at 6 months, and 0.90% (0.3–1.2%) at 1 yr.Of the 95 women with pain 2 months after surgery, 65 (68%) were successfully reached for telephone interview at 6 months. Of these 65 women, 17 (1.4% of the original cohort) reported pain which began at the time of delivery (6 with cesarean and 11 with vaginal delivery, table 2). Pain was identified in a median of two locations per patient, with abdominal scar being the most common location after cesarean delivery and the pelvis after vaginal delivery. Of the 17 women reporting pain at 6 months, only 10 had non-zero scores on the neuropathic pain inventory. The median score was 2.2 (0,5.5) out of a maximum of 10. The number of women with pain 6 months after delivery was not great enough to generate a model of characteristics which predicted pain at this time.Of the 17 women who reported pain at the 6 month interview, 13 (72%) were successfully reached for telephone interview at 12 months. Of the 3 women with pain 12 months after delivery, all had experienced a vaginal delivery (table 3). They had a high burden of pain on activities of daily living and all of them exceeded the threshold of 12 to meet the Edinburgh postpartum depression index for presence of depression (individual values 14, 13, 13). The number of women with pain 12 months after delivery was not great enough to generate a model of characteristics which predicted pain at this time.The canonical correlation analysis optimized the association between each of the theoretical prediction groups (patient characteristics, tissue damage, and pain history) and some aspect of pain after delivery (pain now, average pain, and worst pain). The optimal association was found by weighting each of the predictors in the group by the standardized weights listed in table 1. The weights can be interpreted as the relative importance of that predictor in the uncovered association. For example, lower ratings of state of health (−0.90 weight) along with higher levels of alcohol use prior to pregnancy (0.70), and smoking status (0.36) were the most heavily weighted factors that could account for an evenly weighted representation of the post-delivery pain experience (i.e ., the pain variables were all weighted between 0.32 and 0.43 giving them equal importance in the interpretation). Weighting the predictors in this way created scores that shared R 2= 5.1% of variance in the pain experience, P value less than 0.0001.The pain history predictors were principally pain during pregnancy (0.70 weight), and pain ratings during menstruation (0.44). Interestingly, not seeing a doctor or not receiving medications for pain (−0.43) were also weighted modestly in the association. To achieve the optimal association, the average pain experienced was weighted very heavily (0.86) making a patient’s retrospection of the pain they experienced paramount for this association. Weighting the predictors in this way created scores that shared R 2= 7.0% of variance in the pain experience, P value less than 0.0001.The tissue damage predictors were by giving birth cesarean section weight), with of the other predictors being weighted over To achieve the optimal association, the worst pain experienced was weighted very heavily making this association different than the other predictor Weighting the predictors in this way created scores that shared R 2= of variance in this aspect of the pain experience, P value less than 0.0001.The optimal scores for each of the theoretical were then forced into a regression model to predict the presence of pain and the degree of depressive symptoms at 2 months after delivery. the uncovered associations with of the optimized predictors to predict the presence of pain at 2 months, P than both the patient characteristics, and pain history were to predict the degree of depressive with each in the scores being associated with and in the Edinburgh Post Partum Depression For the associated with the 13 are also presented in half of the labor and delivery, which are associated with or tissue to the Because this experience is and in the and of chronic pain following childbirth could be previous studies with long-term follow-up of new have included pain as a secondary measure have focused on prevalence of pain without whether pain delivery or pregnancy This in our is in the current study which focused on pain which began during the childbirth to be in to other physical two factors to risk of chronic pain after other including surgery, chronic pain and degree of tissue and to the acute and pain after childbirth. These two low incidence of chronic pain and effect of degree of tissue and history of chronic pain on pain, a potential effect of pregnancy or delivery on the response to physical not in chronic pain, there are several to a high incidence of chronic pain from the tissue associated with childbirth. to the and lower preceding labor and delivery, and to of the increased which prior to the onset of because and of by a which also prior to the onset of is associated with and on of including and into the these are to that and and the of chronic pain by tissue in this cesarean delivery, on and and surgical to the lower with also the of chronic contrast to these our study that chronic pain after childbirth is than be expected from the degree of physical For example, the incidence of chronic pain after cesarean delivery in our study is over an of less than that observed after total abdominal or procedures with similar or degree of trauma to the abdominal studies have a higher incidence of pain after childbirth, but these included pain of to the labor and delivery including pain and utilized a scripted telephone interview with simultaneous entry than these new in and is but that some women have reported pain in but not over the some women were lost to and we have no of their incidence of pain from delivery. For this we applied to estimate the likely upper and lower for incidence of pain. the incidence of pain in these estimates still lower than those of abdominal or is not to that chronic pain as a of childbirth or that its are We previously reported that pain and postpartum depression were present in nearly 10% of women 2 months after cesarean or vaginal delivery, associated with with activities of daily to an incidence of 6 weeks after delivery in pain was in our study 6 and 12 months after delivery, those with chronic pain experienced to intensity of pain which was associated with a high of health care and with activities of daily previously that pain at 2 months after delivery was predicted by severity of acute pain within 36 h after the incidence of chronic pain after delivery in the follow-up us from a predictive We factors which increased the of acute post-delivery pain and whether the predictive model applied to pain 2 months after delivery, after the previously described effect of severity of acute pain. We defined a from the of those which likely be related to degree of physical trauma and those related to history of chronic pain. Although degree of tissue to severity of acute pain after delivery, its association was the of this to tissue or a in tissue with childbirth. the of chronic pain on severity of acute pain and pain 2 months after surgery a proportion of women with this or the of the questions Nonetheless, other studies have utilized these to a effect of tissue and chronic pain on these outcome these suggest that either the physical trauma of childbirth, including cesarean delivery, is to produce chronic pain, or that there are or factors during pregnancy or the which nearly chronic pain. studies at the Pain at Wake Forest University of suggest a effect of the from surgical induced with the in a study using telephone we observed an incidence of pain 1 yr after childbirth of to the degree of tissue trauma at delivery and history of chronic pain did not the risk of pain 2 months after delivery, after for the effect of severity of acute pain, they were associated with postpartum These data suggest that chronic pain from childbirth not a major health in the United States and we that the is associated with factors which the risk of chronic pain after physical including

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