Calcium pills tested to boost weak labor contractions

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

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)