Urinary frequency in the first trimester is caused by:
Decreased glomerular filtration rate
Pressure of the enlarging uterus on the bladder
Reduced maternal blood volume
Increased reabsorption of fluid in the kidneys
The Correct Answer is B
Urinary frequency in early pregnancy is due to uterine enlargement exerting pressure on the bladder, combined with hormonal effects of progesterone and 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.
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Related Questions
Correct Answer is C
Explanation
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.
Correct Answer is ["A","B","C"]
Explanation
Renal system changes in pregnancyare driven by increased glomerular filtration rate (GFR), elevated renal plasma flow, and progesterone-mediated smooth muscle relaxation. GFR rises by ~50%, lowering serum creatinine (normal pregnancy 0.4–0.7 mg/dL) and blood urea nitrogen (BUN, normal pregnancy ~8–9 mg/dL). The enlarging uterus compresses the bladder causing urinary frequency. Progesterone relaxes ureters and renal pelvis, leading to dilation (hydronephrosis of pregnancy), urinary stasis, and increased urinary tract infection risk. Mild glycosuria is common due to decreased renal tubular reabsorption but does not always indicate gestational diabetes.
Rationale for correct answers
1.GFR increases significantly during pregnancy due to renal vasodilation and higher plasma volume. This enhances clearance of solutes, resulting in decreased serum creatinine and BUN.
2.Urinary frequency is common, especially in the first trimester due to bladder compression by the uterus and again in late pregnancy when the fetal head engages.
3.Dilation of renal pelves and ureters (hydronephrosis of pregnancy) occurs from progesterone-induced smooth muscle relaxation and uterine compression, causing urinary stasis and increased risk of UTI.
Rationale for incorrect answers
4.Serum creatinine and BUN do not increase in pregnancy. Both decrease due to increased GFR. Elevated values indicate abnormal renal function or preeclampsia.
5.Glycosuria is common due to increased filtered glucose load exceeding tubular reabsorptive capacity. It is not diagnostic of gestational diabetes unless persistent and associated with abnormal glucose tolerance testing.
Take home points
• GFR rises by ~50% in pregnancy, lowering creatinine and BUN levels.
• Urinary frequency occurs from uterine pressure on the bladder.
• Hydronephrosis of pregnancy predisposes to urinary tract infections.
• Mild glycosuria is common and not always diagnostic of gestational diabetes.
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