Physiology and clinical value of glycosuria after a glucose challenge during pregnancy

Urine testing for glucose is commonly performed during pregnancy but little is known about the regulation and clinical value of glycosuria because studies are hampered by its low prevalence and intermittent nature. The aim of this study was to compare the urine and plasma response 60 min after a 50 g oral glucose challenge in the setting of gestational diabetes mellitus (GDM) screening.

Of 338 consecutively enrolled gravidas, 325 completed the study. Glycosuria was measured semi-quantitatively (0, 1, 2 or 3+) and venous plasma glucose was measured.

Post-challenge glycosuria occurred in 26.2% of gravidas. Women with 2 or 3+ glycosuria showed higher plasma glucose (p<0.001), lower height (p=0.004) and lower body weight throughout pregnancy (p=0.014); however, glycosuria was not related to age, parity, body mass index (BMI), highest blood pressure or newborn size at birth. The sensitivity for a GDM diagnosis was 8.2%. Comparison of pure "urine" responders (i.e., any glycosuria but glucose <130 mg/dl, n=50) with "plasma" responders (no glycosuria but plasma glucose >or=140 mg/dl, n=29) showed that urine responders were younger and had a lower body weight and BMI than plasma responders.

Glycosuria after an oral glucose challenge depends on the plasma glucose excursion, and is more pronounced in gravidas with lower height and body weight, who presumably have a smaller plasma distribution volume. Post-load glycosuria is a poor predictor of GDM, pre-eclampsia and newborn size at birth, and therefore has limited clinical benefit.