Oral calcium carbonate as an adjunct to oxytocin infusion for labor induction: a randomized controlled pilot study on feasibility and acceptability

Abstract

Background

Calcium carbonate supplementation may offer a simple, low-cost adjunctive benefit to synthetic oxytocin that could enhance the effectiveness of medical labor induction, reduce associated risks, and improve outcomes for both mother and baby. However, its potential role as an adjunct uterotonic remains understudied.

Objective

This study aimed to assess the feasibility and acceptability of conducting a large randomized controlled trial evaluating the effect of coadministering oral calcium carbonate with synthetic oxytocin infusion during labor induction on labor and delivery outcomes.

Study Design

This randomized, controlled, open-label pilot study included nulliparous women with a singleton pregnancy at ≥36 weeks of gestation, a healthy fetus in cephalic presentation, and a planned induction or augmentation of labor with synthetic oxytocin (Pitocin). Patients were excluded if their fetal monitoring showed recurrent fetal heart rate decelerations or tachysystole in the 30 minutes prior, if they had a planned cesarean delivery, a known contraindication to calcium carbonate, or were receiving treatment with calcium channel blockers or magnesium. Participants were randomized in a 1:1 ratio to receive either synthetic oxytocin alone (control) or oral calcium carbonate coadministered with oxytocin (intervention). The intervention group was assigned to receive 500 mg of calcium carbonate every 4 hours, starting at the initiation of oxytocin infusion. Labor characteristics and outcomes were recorded. The primary outcomes were feasibility and acceptability measures: recruitment, enrollment, and adherence rate to the study protocol.

Results

From November 18, 2024, to October 16, 2025, 182 patients were screened for study eligibility. Of these, 137 met eligibility criteria (75%), and 122 (89%) were approached by available research staff. A total of 59 patients (48% of those approached) consented, and 55 participants were randomized: 26 were assigned to receive standard care oxytocin infusion, and 29 were assigned to receive oral carbonate in combination with oxytocin infusion. One patient randomized to the control group underwent cesarean delivery for nonreassuring fetal status prior to oxytocin administration, and one patient randomized to calcium carbonate delivered prior to intervention start; both patients were therefore excluded from analysis. All other participants adhered to their assigned intervention. Among those in the calcium carbonate group, the median number of tablets administered calcium carbonate was 3 tablets (range 2–4). Although not powered for clinical outcomes, exploratory analyses suggest trends toward a higher frequency of spontaneous vaginal delivery, shorter time to delivery, and lower oxytocin exposure, including shorter duration and lower maximum dose, in the calcium carbonate group compared to the control group.

Conclusion

Random allocation to standard care, oxytocin, or calcium carbonate in combination with oxytocin for labor induction was feasible and acceptable to patients and clinicians.