A pregnant woman at 20 weeks of gestation has a random plasma glucose of 130 mg/dL and dipstick-positive glycosuria on two occasions. She has no ketosis and HbA1c is normal. The most likely explanation for her glycosuria is:
- A Reduced glomerular filtration of glucose due to raised oncotic pressure
- B Primary downregulation of SGLT2 transporters by placental hormones
- C Increased GFR raising the filtered glucose load above the tubular maximum ✓
- D Impaired passive glucose diffusion across the proximal tubular epithelium
Correct answer: C. Increased GFR raising the filtered glucose load above the tubular maximum
Explanation
Pregnancy raises GFR by about 50 percent, so the filtered load of glucose rises even at normal plasma levels and can transiently exceed the tubular reabsorptive capacity, producing benign gestational glycosuria. Because the Tm for glucose is about 375 mg/min while the usual renal threshold corresponds to a plasma level near 180 mg/dL, a higher filtered load alone can spill glucose without any transporter defect. SGLT2 activity itself is not suppressed in this setting.
Reference: Ganong Review of Medical Physiology, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.