Glycosuria is more common during pregnancy because of the lowering of the renal threshold for glucose excretion.
The increase in the glomerular filtration rate delivers an overwhelming glucose load to the renal tubules. Reabsorption, which is normally complete, is thus compromised.
A loss of 140 mg glucose per day of glucose is the usual upper limit. Losses may reach 1 g/day.
There is a diurnal variation in glycosuria: being least evident in the morning and most evident after meals.
Women who develop diabetes during pregnancy are said to have gestational diabetes. Some will remain diabetic after delivery of the foetus while others will revert to apparent normality. The detection of gestational diabetes is described (1):
NICE suggest testing criteria for gestational diabetes as:
- use the 2-hour 75 g oral glucose tolerance test (OGTT) to test for gestational diabetes in women with risk factors (see below)
- offer women who have had gestational diabetes in a previous pregnancy:
- early self-monitoring of blood glucose or
- a 75 g 2-hour OGTT as soon as possible after booking (whether in the first or second trimester), and a further 75 g 2-hour OGTT at 24-28 weeks if the results of the first OGTT are normal
- offer women with any of the other risk factors for gestational diabetes a 75 g 2-hour OGTT at 24-28 weeks (see below)
- glycosuria detected by routine antenatal testing
- be aware that glycosuria of 2+ or above on 1 occasion or of 1+ or above on 2 or more occasions detected by reagent strip testing during routine antenatal care may indicate undiagnosed gestational diabetes. If this is observed, consider further testing to exclude gestational diabetes
- risk factors for gestational diabetes:
- BMI above 30 kg/m2
- previous macrosomic baby weighing 4.5 kg or above
- previous gestational diabetes
- family history of diabetes (first-degree relative with diabetes)
- minority ethnic family origin with a high prevalence of diabetes
- diagnosis of gestational diabetes
- diagnose gestational diabetes if the woman has either:
- a fasting plasma glucose level of 5.6mmol/litre or above or
- a 2-hour plasma glucose level of 7.8mmol/litre or above
Reference: