Associations between postpartum pain, mood, and maternal–infant attachment and parenting outcomes

The University of Pittsburgh Institutional Review Board approved the study (PRO15030338) and written informed consent was obtained from all participants. All methods were conducted in accordance with relevant guidelines and regulations including CONSORT 2010 guidelines. Data supporting the findings of this study are available from the corresponding author, but restrictions apply to the availability of these data which were used under license for the current study so are not publicly available. The datasets used and analyzed during the current study available from the corresponding author on reasonable request.

Patients

Pregnant women receiving perinatal care at the University of Pittsburgh Medical Center Magee-Women’s Hospital, or The Midwife Center for Birth and Women’s Health (Pittsburgh, PA, USA) were screened and approached if eligible at their third trimester prenatal clinic visit. After providing written informed consent, women planning on spontaneous labor or scheduled induction of labor at term gestation were enrolled. Inclusion criteria were presentation to our labor and delivery unit at ≥ 38 weeks gestation and complete baseline inventories. Exclusion criteria were age < 18, non-English speaking as surveys were validated in the English language, chronic pain history, taking medication for opioid use disorder, severe obstetric disease (i.e., pre-eclampsia or eclampsia requiring magnesium therapy, necessity for immediate cesarean delivery without labor), class 3 obesity with body mass index ≥ 40 kg/m², fetal anomalies or growth restriction, contraindications to neuraxial anesthesia, inability to follow the study protocol for 3 months, admission for labor and delivery not at term gestation, and plans for newborn adoption.

Demographic and obstetric data and patient-reported instruments

Self-reported demographic characteristics were completed, and obstetric and labor characteristics were collected from the medical record. Variables included race, ethnicity, mode of delivery, epidural analgesia utilization in labor. We also recorded history of abuse (i.e., partner, sexual, domestic, and childhood abuse), as well as histories of substance abuse, anxiety, depression, and other mental illness. Participants electronically completed prenatal assessments of depression (Edinburgh Postnatal Depression Scale, EPDS), anxiety (State-Trait Anxiety Inventory, STAI)^{2, 14}, resiliency (Ego-Resiliency Scale, ER-89)¹⁵, and pain catastrophizing (Pain Catastrophizing Scale, PCS)¹⁶, multidimensional scale of perceived social support (MSPSS), and a pain inventory (Brief Pain Inventory—Long Form, BPI-L)¹⁷. These variables were selected based on validated associations with pain, depression, or both^{17, 18}. Pain (BPI Short Form, BPI-S), and perceived stress scale (PSS) were recorded on the first or second postpartum day. At six weeks postpartum, participants completed the EPDS, BPI-S, the maternal parent attachment scale (MPAS), the parenting self-efficacy (PMP-SE), and the Ages and Stages Questionnaire (ASQ) for two months (ASQ-2 months). At three months postpartum, participants were administered the EPDS, the BPI-S, the ASQ-4 months. The ASQ-2 months and -4 months were used at 6 weeks and 3 months respectively. The four timepoints considered were baseline and postpartum day 1, 6 weeks postpartum, and 3 months postpartum.

EPDS is a self-completed, 10-item scale developed specifically for women in the perinatal period. It was shown to identify patients at risk for perinatal depression^{1, 19}. It is essential to note that EPDS not intended to substitute for a mental health professional’s diagnosis of depression; it has estimated 80% sensitivity for the diagnosis^{1, 19}. Nevertheless, because it is not as specific as other instruments, the EPDS might identify some women who are not depressed. Therefore, the scale should be used to screen patients appropriate for specialist referral^{1, 20}. The State-Trait Anxiety Inventory (STAI) is a psychological inventory consisting of 40 self-report items on a 4-point Likert scale. The STAI measures two types of anxiety—state anxiety and trait anxiety. Higher scores are positively correlated with higher levels of anxiety. The Brief Pain Inventory—Short Form (BPI-SF) is a 9-item self-administered questionnaire used to evaluate the severity of a patient’s pain and the impact of this pain on the patient’s daily functioning. The Perceived Stress Scale (PSS) is a stress assessment instrument consisting of 10 items with stress-related questions. The Pain Catastrophizing Scale (PCS) assesses the extent of catastrophic thinking. It is a 13-item scale, with a total range of 0 to 52. Higher scores are associated with higher amounts of pain catastrophizing. The Maternal Postnatal Attachment Scale (MPAS) is a 19-item self-report questionnaire that is used to assess mother-to-infant attachment. Maternal Parenting Self-Efficacy (PMP S-E) has 20 items rated with a four-point scale ranging from 1 (strongly disagree) to 4 (strongly agree). Higher scores indicate higher levels of perceived self-efficacy. The Ages and Stages Questionnaires (ASQ) are composed of 5 components each has 6 questions completed by parents, evaluating infant and child development.

Statistical analysis

The primary predictor of interest was “pain right now” assessed by the BPI on a 0–10 numeric rating scale where 0 is “no pain” and 10 is “pain as bad as you can imagine” (corresponding questions #15 on the BPI-L at baseline and #6 on the BPI-S at postpartum days 1, 6 weeks, and 3 months). The primary outcomes were MPAS and PMP-SE at 6 weeks and 3 months. Univariate regression explored the associations between the outcomes of MPAS and PMPSE at 6 weeks and 3 months, and the predictor variables for pain, mood (anxiety, STAI; depression, EPDS), epidural analgesia use, catastrophizing (PCS), social support (MSPSS), perceived stress (PSS), and resiliency. Interaction terms were assessed for any pain and mood predictor variables that met the significance threshold of P < 0.10 in univariate analyses.

Generalized linear model analysis

General linear modeling was used to explore the relationship between the primary predictor of “pain right now” at baseline (measured by the BPI) and other baseline covariates (age, perceived stress by MSPSS, anxiety by STAI, depression by EPDS), for the outcomes of parenting (maternal–infant attachment scale by MPAS and parenting self-efficacy by PMPSE) and child development (ages and stages questionnaire 3rd edition, ASQ-3) at 6 weeks and 3 months postpartum.

Sample size calculation

As a pilot study, we targeted 10% of the sample required for a full study that would evaluate primary relationships between postpartum pain and depression. The presumed baseline incidence of postpartum depression in American women was 10–20%. For a full study, based on previous work that compared non-epidural pain relief during delivery and postpartum depression, a sample size of 400 in each group (excessive pain versus limited pain) would have 80% power to detect a 10% difference in postpartum depression between groups with a significance level (alpha) of 0.05 (two-tailed). Accounting for an estimated dropout rate of 15%, we expected expect to enroll a total of 430 subjects in each group. The risk for postpartum depression was defined by a positive screen (score ≥ 10) on the EPDS tool. Therefore, we targeted a sample size of 86 patients, as would yield 10% of the sample size required for a full study.

Statistical analyses were performed using StataSE (version 17.1, College Station, TX), Excel (version 16.35, Microsoft), and SAS, version 9.4 statistical software (SAS Institute Inc., Cary, NC). Descriptive statistics were presented as means (standard deviations), medians (with 25th and 75th percentiles) for continuous data and as absolute frequencies and percentages for categorical data.