Childbirth is a natural process, but can result in long term maternal morbidity. Additionally, CD represents major surgery and surgical trauma. The current study suggests that pain during the immediate period after delivery, a time typically of relaxed attention to patient care, is an important contributor to significant persistent pain and depression after childbirth. Our data suggest that these morbidities are not primarily related to the degree of physical trauma, as grossly measured by cesarean compared to vaginal delivery, but rather are related to the individual's pain response to that injury. Although some variables associated with persistent pain after surgery, including anxiety, were not assessed in this study and included in the propensity analysis, the large sample size suggests that mode of delivery is extremely unlikely to represent an important risk factor for this outcome. This hypothesis is consistent not only with the current study, but with an emerging literature on inter-individual differences in pain following surgical trauma [13
]. Several important implications follow from these observations.
We focused our evaluations at 2 months after delivery, since this is the time of peak prevalence of postpartum depression [19
]and because pain at this time after surgery correlates with chronic pain [13
]. Additionally, pain and depression 2 months after delivery represent important health outcomes and public health burdens in their own right. Early postpartum depression increases the risk of insecure infant attachment and cognitive and behavioral problems in children [24
], and suicide in mothers with postpartum depression accounts for 17% of late pregnancy-related death [10
]. We did not determine whether depression was present in women prior to delivery, and it is conceivable that some women classified in our sample as postpartum depression had chronic depression. Although the incidence of post-partum depression is similar to that of the female US population as a whole, it is distinguished by its onset, typically within the first 6 weeks after delivery. Prior depression carries a relative risk of approximately 2.0 for postpartum depression [22
]. As such, we would anticipate that a small minority of those identified in our sample with post-partum depression had preexisting depression prior to delivery.
Of patients in the current study with persistent pain at 8 weeks postpartum, 36% after CD and 60% after VD reported constant or daily pain, with half of them having difficulty performing normal daily activities, and 33 to 50% of them having their mood and/or ability to sleep negatively affected. This persistent pain might limit these mothers' ability to cope with the multiple stresses facing women shortly after delivery. These reported impacts of pain may underestimate the problem because mothers frequently do not disclose such problems because of embarrassment or lack of appropriate descriptive language even though they would like more advice and assistance [5
Although persistent pain and depression were clearly associated, the model resulting from this study indicates independent risks for each of these morbidities from severity of acute pain (). Studies in animals suggest that acute intervention at the time of tissue trauma reduces the likelihood that chronic pain will develop [12
]. Several interventional clinical trials are underway in surgical patients to test the hypothesis that the severity of acute pain is not merely a marker of chronic pain development, but actively participates in the pathophysiology of the transition from acute to chronic pain. The current study adds women after childbirth to those who may benefit from testing this hypothesis.
Variability in tissue trauma undoubtedly contributed to the large inter-individual variability in acute postpartum pain in the current study. However, similarly large variability in post-procedural pain among patients after similar, relatively standardized procedures, such as abdominal hysterectomy [4
] or elective CD [18
], suggests that factors other than the degree of tissue trauma contribute importantly to this variability. Although increased anxiety and degree of somatization are associated with increased individual assessment of pain after surgery, the strongest and most consistently observed predictor is sensitivity to an experimental stimulus [13
]. Intrinsic factors controlling or modulating the response to painful stimuli, including genetic factors [8
] likely contribute importantly to this variability. The current study highlights the need to further develop models to predict who will have significant acute and/or persistent pain after delivery.
We observed a high prevalence of severe acute pain after childbirth confirming that many hospitalized patients continue to experience moderate to severe postoperative and postpartum pain [2
]. Based on this study, nearly 500,000 American women may experience severe acute pain after childbirth annually. It is arguably more important for new mothers than for patients after other procedures to receive adequate pain treatment because of the demand for their prompt return to activities, bonding with and caring for the newborn. Although few would openly argue against good pain control for new mothers, recent events have erected barriers in addition to those common to the treatment of other forms of acute post traumatic pain. Opioids and nonsteroidal anti-inflammatory drugs, mainstays of treatment for moderate to severe acute pain, carry warnings against their use in breastfeeding women [1
]. Additionally, considerably less attention is paid to non-pharmacologic approaches to analgesia after delivery than before. The current study argues strongly for focusing more attention on improving pain control and increasing the options for pain control after childbirth, not just during childbirth.
In conclusion, 1 of 5 women after CD and 1 of 13 after VD in US tertiary care centers suffer from severe acute pain after delivery. Severity of acute postpartum pain, but not mode of delivery, imparts a large and independent risk for persistent pain and depression, with negative effects on activities of daily living and on sleep. These observations suggest the need to direct more of our focus to better management of acute pain during the first few days following childbirth in order to prevent longer term morbidities and to improve outcomes, not only for women after CD, but also for those after VD. Research is needed to define predictive factors for severe acute post-delivery pain and investigate therapeutic interventions in this high risk sub group that would reduce persistent pain and depression during this vulnerable period of the first few months after delivery.