Clinical effectiveness of the Circle of Security-Parenting group intervention for birthing parents in perinatal mental health services in England (COSI): a pragmatic, multicentre, assessor-masked, randomised controlled trial.

backgroundPerinatal mental health difficulties are common and, if untreated, are associated with long-term adverse child outcomes. Substantial evidence gaps exist in group-based and parent-infant interventions for perinatal mental health difficulties. Circle of Security-Parenting (COS-P) groups have shown preliminary efficacy, although previous studies were methodologically weak or not specific to relevant populations. This study aimed to evaluate whether the hybrid delivery of COS-P plus treatment-as-usual reduces psychopathology in birthing parents accessing National Health Service community perinatal mental health services, compared with treatment-as-usual alone.

methodsThe study was a pragmatic, multicentre, parallel-arm, assessor-masked, randomised controlled trial, with an internal pilot. Participants were recruited from ten geographically spread National Health Service (NHS) Trusts across England, including in Cheshire, Merseyside, North and South Yorkshire, Cumbria, Northamptonshire, Devon, Sussex, and Hampshire. Sites were eligible if they had a specialist community perinatal mental health service and had clinical equipoise to delivering COS-P. Participants were eligible for inclusion if they were aged 18 years or older; receiving care from the participating community perinatal mental health service sites between January, 2021, and October, 2023; had clinical-level psychopathology (average Clinical Outcomes in Routine Evaluation-Outcome Measure [CORE-OM] ≥1·1); bonding difficulties (total Postpartum Bonding Questionnaire ≥12); and were the birthing parent of a child aged younger than 1 year. Participants currently experiencing active psychosis were excluded. Participants were randomly assigned (2:1) to COS-P plus treatment-as-usual or treatment-as-usual alone. Randomisation was stratified by recruitment site and cohort, with random allocation lists generated in advance. Investigators and assessors were masked. COS-P is an attachment-informed parenting group delivered in ten 90-min sessions, predominantly online. The primary outcome was psychopathology, assessed by the average CORE-OM score across all follow-up timepoints of 3 months, 7 months, and 12 months post-baseline. Analyses followed the intention-to-treat principle and sensitivity analyses were done using multiple imputation to account for missing data. People with lived experience were involved in the design, delivery, and dissemination of the trial. This study is registered as an International Standard Randomised Controlled Trial, ISRCTN18308962, and was completed in January, 2025.

findingsBetween Jan 4, 2022, and Oct 26, 2023, 3171 individuals were screened for eligibility, 2785 were ineligible, and 371 were randomly assigned to a group (248 to the COS-P plus treatment-as-usual group and 123 to the treatment-as-usual group. All participants were assigned female at birth and were the birthing parent to the index child. 332 (89%) participants identified as women (including trans woman), five (1%) identified as non-binary, one (<1%) in another way, three (1%) preferred not to say, and 30 (8%) had missing gender identity data. The mean age of participants was 30·8 years (SD 5·4; range 19-44); 329 (89%) were of White ethnicity. The adjusted mean difference in psychopathology scores, averaged across the 3-month, 7-month, and 12-month follow-up points, was -1·41 (95% CI -5·11 to 2·28; p=0·45), indicating neither clinical nor statistical significance. No significant differences were identified in secondary outcomes. Commonly reported adverse events included increases in mental health difficulties or symptoms, affecting 16 participants (4%); self-harm or concerns about self-harm, affecting 11 (3%) participants; and eye strain following screen use for study activities, affecting 11 (3%) participants. Serious adverse events were reported by eight (2%) participants.

interpretationCOS-P plus treatment-as-usual did not demonstrate greater clinical effectiveness compared with treatment-as-usual alone when delivered in NHS community perinatal mental health services. Therefore, COS-P should not be recommended for inclusion in routine community perinatal mental health services care, as it does not provide any additional clinical benefit when added to the current treatment-as-usual available in improving parental psychopathology, parenting, or infant outcomes.

fundingNational Institute for Health and Care Research Health Technology Assessment programme.