Calcium Carbonate to Augment Labor Contractions

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)