A nurse in a prenatal clinic is caring for a client who is at 12 weeks gestation. The client asks about the cause of her heartburn. Which of the following responses should the nurse make?

A. At 12 weeks, the uterus is still within the pelvis, so it does not significantly compress the stomach. Uterine pressure becomes a major contributor to heartburn later in pregnancy. B. Retained bile in the liver is not a typical cause of heartburn; bile primarily affects fat digestion and does not directly cause gastroesophageal reflux. C. Increased estrogen does not significantly increase hydrochloric acid secretion. Heartburn is primarily related to mechanical and hormonal changes, not excess acid production. D. Increased progesterone levels during pregnancy relax smooth muscle, including the lower esophageal sphincter. This relaxation allows stomach acid to reflux into the esophagus, leading to heartburn. Progesterone also slows gastrointestinal motility, further contributing to discomfort.