The goal of this clinical trial is to learn if oral calcium carbonate can improve uterine contractions and labor outcomes in term pregnancies. It will also evaluate the safety of calcium carbonate when used during labor. The main questions it aims to answer are:

Does oral calcium carbonate increase uterine contraction strength? Does it lead to shorter labor duration or higher vaginal delivery rates? What side effects or complications, if any, occur with calcium carbonate use during labor?

Researchers will compare oral calcium carbonate to no treatment to see if it helps improve labor efficiency and reduce cesarean delivery rates.

Participants will:

Be randomly assigned to receive either 2,000 mg of oral calcium carbonate or no intervention Undergo monitoring with an intrauterine pressure catheter to measure contraction strength Be observed for two hours without oxytocin to assess calcium's direct effect on contractions Have data collected on labor progression, delivery outcomes, and neonatal health

In the United States, nearly one-third of deliveries are performed via cesarean section, with labor dystocia remaining a leading indication. Labor dystocia may result from a variety of maternal and fetal factors, including malposition, cephalopelvic disproportion, or ineffective uterine contractions. When contractions are inadequate, the standard intervention is intravenous oxytocin. However, prolonged or high-dose oxytocin administration can lead to receptor desensitization, reducing its effectiveness and increasing the risk of postpartum hemorrhage.

Calcium plays a key role in myometrial contractility by facilitating calcium influx through L-type channels in myometrial cells, which triggers intracellular calcium release and action potentials. During labor, upregulation of calcium channels enhances the uterus's responsiveness to contractile stimuli. Elevated serum calcium levels have been associated with stronger and more effective contractions.

Adjunctive intravenous calcium administration with oxytocin has been shown to improve labor outcomes, including higher rates of vaginal delivery within 24 hours of induction and reduce blood loss in cesarean deliveries. However, the potential role of oral calcium supplementation in enhancing labor progression has not been evaluated in clinical trials. Given its physiological relevance, accessibility, and low-risk profile, oral calcium may represent a simple adjunct to improve labor efficiency and reduce cesarean rates.

This study aims to evaluate the impact of oral calcium carbonate supplementation during labor on uterine contractility and clinical outcomes. The investigators hypothesize that calcium carbonate administered intrapartum will enhance uterine contractions, resulting in higher vaginal delivery rates, shorter time to delivery, and reduced blood loss.

Inclusion Criteria:

• Had an intrauterine pressure catheter in place
• Term gestation, greater than or equal to 37 weeks of gestation
• Singleton pregnancy
• Cephalic presentation
• > 18 years of age

Exclusion Criteria:

• incarceration
• multiple gestation
• active illicit drug use
• abnormal clinical pelvimetry
• Suspected fetal macrosomia defined as estimated fetal weight ≥4250 grams
• intrauterine growth restriction
• abnormal placentation
• prior cesarean delivery
• maternal history of arrhythmia
• hyperparathyroidism
• heart failure
• renal or hepatic failure
• nephrolithiasis
• receipt of medications known to affect uterine contractility-such as magnesium sulfate, terbutaline, or recent misoprostol in the last four hours

Study has already been completed, will analyze data first and then decide