Rationale, design, and statistical analysis plan for a randomized, double-blind, placebo-controlled trial of Limosilactobacillus reuteri to support mother-infant bonding and maternal socioemotional functioning in postpartum women at increased risk for postpartum depression.

BACKGROUNDPostpartum depression (PPD) is common and can impair early mother-infant bonding. Oxytocin (OXT) supports socioemotional adaptation, yet intranasal OXT yields supraphysiological exposure and mixed results. The probiotic Limosilactobacillus reuteri (L. reuteri) increases endogenous oxytocin levels in rodents, suggesting that it may enhance OXT signaling via gut-brain pathways in humans. We designed a proof-of-concept trial to test whether postpartum L. reuteri improves early mother-infant bonding and maternal mental health, impulse control, and emotion recognition.

METHODSIn this randomized, double-blind, placebo-controlled trial, mothers aged ≥18 years at elevated PPD risk (history of depression, prior PPD, and/or increased prenatal depressive symptoms) received 6 weeks of once-daily L. reuteri or placebo, stratified by delivery mode (vaginal/Cesarean section). The primary endpoint is mother-infant bonding quality at Week 6; secondary endpoints include maternal mental health, impulse control, and emotion recognition at Week 6. Salivary OXT at Week 2 serves as a mechanistic endpoint.

RESULTSForty-six participants (mean age ± SD: 34.3 ± 4.5 years) were enrolled and randomized; 38 (82.6%) completed the Week-6 visit. Baseline characteristics are reported.

CONCLUSIONThis trial evaluates whether a lactation-compatible L. reuteri intervention targeting endogenous OXT improves early mother-infant bonding and maternal well-being. Findings will inform feasibility, safety, and effect size estimates, clarify OXT's mechanistic role in PPD pathophysiology, and guide development of microbiome-based therapeutics for perinatal mental health.

TRIAL REGISTRATION NUMBERClinicalTrials.gov: NCT04472065.