I am involved in the care of many patients with gestational diabetes (usually low income women in their 20s who are obese). I have seen statements about glycosuria being present if the blood glucose is over 180 mg/ dl (10 mmol/L). Is there any general rule about when glucose is spilled in pregnant women with normal kidney function?

During pregnancy, the threshold for clearance of glucose through the kidney is lowered. This may be related to increased renal perfusion due to increased circulating blood volume. In addition, the kidney enlarges slightly during pregnancy. I was not able to find any statement relating glycosuria to blood glucose value. From my experience, I have noted that the presence of glucose in the urine is not overly useful information. If a mother without diabetes has a bowl of sugar-coated cereal for breakfast, she may have subsequent glucosuria. Nevertheless, if a mother has recurrent glucose in her urine, then screening for diabetes is worthwhile.

OWJ