Adult Antacids--therapeutic use Anti-Ulcer Agents--therapeutic use Cesarean Section Citrates--therapeutic use Citric Acid Drug Therapy, Combination Emergencies Female Gastric Acid Gastrointestinal Contents--drug effects Humans Hydrogen-Ion Concentration--drug effects Metoclopramide--therapeutic use Omeprazole--therapeutic use Pneumonia, Aspiration--prevention & control Postoperative Complications--prevention & control Pregnancy Ranitidine--therapeutic use