Which of the following gastrointestinal changes is typically attributed to the relaxation of the lower esophageal sphincter by progesterone?

Urinary frequency in early pregnancyis due to uterine enlargementexerting pressure on the bladder, combined with hormonal effects of progesteroneand estrogen. Normal glomerular filtration rate (GFR) in non-pregnant adults is 90–120 mL/min, but in pregnancy, GFR actually increases by about 50% starting early in the first trimester. Plasma volume rises by 40–50%, and renal plasma flow increases by 50–80%, both enhancing urinary output. However, in the first trimester, the uterus remains a pelvic organ, directly compressing the bladder, leading to urinary frequency.

Rationale for correct answer

2.The enlarging uterus in the first trimester sits in the pelvis and presses on the bladder, reducing bladder capacity and causing urinary frequency. This mechanical pressure is the primary cause in early pregnancy before the uterus ascends into the abdominal cavity.

Rationale for incorrect answers

1.GFR does not decrease in pregnancy; instead, it increases significantly due to renal vasodilation and increased plasma volume. A decreased GFR would lower urine output, not increase urinary frequency.

3.Maternal blood volume does not reduce in pregnancy; it progressively increases by 40–50% to meet fetal and maternal needs. A reduced blood volume would impair renal perfusion, leading to oliguria, not urinary frequency.

4.Increased tubular reabsorption of fluid conserves body water and would reduce urine production. In pregnancy, although sodium and water retention occur, they do not directly cause urinary frequency in the first trimester.

Take home points

• First-trimester urinary frequency results from uterine pressure on the bladder.

• GFR increases in pregnancy, leading to greater renal clearance, not reduction.

• Maternal blood volume expands, not decreases, in pregnancy.

• Fluid reabsorption increases to maintain volume but does not cause frequency.

Heartburn (pyrosis)occurs in pregnancy mainly due to progesterone-induced relaxationof the lower esophageal sphincter. This hormone lowers smooth muscle tone, allowing gastric acid to reflux into the esophagus. Symptoms include burning sensation behind the sternum, worsened after meals or lying down. Normal lower esophageal sphincter pressure ranges between 10–30 mmHg, but pregnancy reduces it to below 10 mmHg. Risk factors include increased intra-abdominal pressure from the enlarging uterus and delayed gastric emptying. Complications include esophagitis and sleep disturbance.

Rationale for correct answer

3.The presence of heartburn (pyrosis) in pregnancy is directly linked to progesterone’s smooth muscle relaxation, causing reduced lower esophageal sphincter tone and gastric acid reflux. The clinical presentation is a burning retrosternal discomfort, especially worsened after meals or lying supine. This directly aligns with the pathophysiology described.

Rationale for incorrect answers

1.Pica is an abnormal craving for non-nutritive substances like clay or ice. It is associated with iron deficiency anemia, not progesterone-induced smooth muscle relaxation. Its pathophysiology relates to altered dopamine pathways and iron metabolism, not gastrointestinal sphincter tone.

2.Constipation is common in pregnancy but results from decreased intestinal peristalsis due to progesterone and increased water absorption in the colon. It is not caused by relaxation of the lower esophageal sphincter but rather delayed transit time within the intestines.

4.Gingivitis in pregnancy is due to vascular changes and exaggerated inflammatory response to dental plaque under high estrogen and progesterone levels. It involves gum swelling, bleeding, and hyperemia, not esophageal sphincter relaxation.

Take home points

• Progesterone lowers lower esophageal sphincter pressure, leading to gastroesophageal reflux and heartburn.

• Constipation in pregnancy results from delayed intestinal transit, not sphincter relaxation.

• Gingivitis is hormonally mediated gum inflammation, unrelated to esophageal sphincter physiology.

• Pica is associated with iron deficiency anemia, not gastrointestinal smooth muscle tone changes.