The investigators think that calcium carbonate can act as an assistive medication to improve contractions during labor.

This study plans to study the acceptance and safety of using calcium carbonate as an medicine to help the labor induction process. The study aims to find if the use of calcium carbonate will lead to better labor contractions and increase the percentage of vaginal deliveries and improve delivery outcomes.

Inclusion Criteria:

• 18 years or older
• Nulliparas (no prior pregnancy lasting 20 weeks or greater of gestation)
• Gestational age above 36 weeks, at enrollment
• Present for induction or augmentation of labor inclusive of medical indication, elective induction at greater than 39 weeks' gestation, trial of labor after cesarean
• Singleton gestation (a multiple gestation reduced to a singleton, either spontaneously or therapeutically, before 14 0/7 weeks of gestation is acceptable)
• Ability to give informed consent
• Planned to undergo initiation of oxytocin infusion by their maternity care provider

Exclusion Criteria:

• Unable to understand or read English
• Presence of tachysystole (defined as more than 5 contractions in 10 minutes averaged over 30 minutes), recurrent variable or late fetal decelerations, and bradycardia in the prior 30 minutes before enrollment
• Non-vertex presenting fetus at enrollment
• Planned for cesarean delivery or contraindication to labor by institutional policy (e.g., placenta previa, vasa previa, active genital herpes infection, previous transmural myomectomy)
• Multi-fetal gestation (twins, triplets, and higher order multiples)
• Known contraindication to taking calcium carbonate including renal calculus, high urine calcium levels, elevated serum calcium, low serum phosphate, achlorhydria, or suspected digoxin toxicity.
• Deliveries with fetal chronic and/or pregnancy-related conditions, IUFD (Intra Uterine Fetal Death) or premature < 36 weeks of gestation.
• Major fetal anomaly suspected prenatally (defined as a fetal anomaly with anticipated neonatal intensive care unit admission)
• Suspected alloimmunization (given the increased likelihood for anticipated neonatal intensive care unit admission)
• Known severe fetal growth restriction (estimated fetal weight <3rd percentile) or abnormal umbilical artery Doppler studies (given the increased likelihood for anticipated neonatal intensive care unit admission)
• Participation in another interventional study that influences management of labor and delivery or perinatal morbidity or mortality
• Known allergic reactions to synthetic oxytocin intravenous solution or to Calcium Carbonate
• Significantly impaired consciousness or executive function (e.g., intubated or sedated)
• Patients treated with calcium channel blockers such as nifedipine or magnesium.
• Chronic renal failure and hyperphosphatemia.
• Inability to tolerate oral intake (i.e., nausea/vomiting)

Data Analyst will be masked to the interventions assigned to participants.