Methodologic Concerns Regarding a Study Concluding That Epidural Labor Analgesia Is Associated with a Decreased Risk of Postpartum Depression

摘要

To the Editor We advance the following concerns with the observational study of epidural analgesia and postpartum depression (PPD) by Ding et al.: Inadequately Addressed Bias1. Misclassification bias: Although defined as such, the study by Ding et al.1 does not meet the definition of a prospective cohort, because their sample was not depression-free at the time of exposure. The authors do not estimate the magnitude and direction of this misclassification bias on their findings. Given that the prevalence of depression is 20% among Chinese women, and that depressed women are less likely to advocate for pain control, the study results could be moderately biased toward a protective effect. 2. Selection bias: Obese subjects were excluded without clear justification. Obesity is not a contraindication for epidural analgesia and is actually associated with an increased incidence of epidural and a greater risk of PPD. The study reports a negative association between epidural analgesia and PPD. Given the proportion of obese women who were excluded (35% of the final sample size), there may be substantial bias in the direction of a significant protective association between epidural analgesia and PPD. Second, the authors present a greater loss to follow-up among the epidural group than the nonepidural group (24 vs 13). The reasons cited for this differential loss include known risk factors for PPD, namely, "too tired after delivery" and "bad mood because infant in the neonatal intensive care unit." Evidence shows that mothers of infants admitted to neonatal intensive care unit have greater-than-average rates of depression and anxiety. It is well established that patients with depression are more likely to be lost to follow-up. In Chinese society, the family makes medical decisions rather than the individual. Thus, the family's refusal to continue with the study could reflect their concern for the mother's mental health.