Finding the right tests…
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Finding the right tests…
Glucose
BLOOD SUGAR 3 HOURS is the last of four samples taken in the 100-gram, two-step gestational diabetes protocol — the only routine glucose test in this family that runs a full three hours. By this point, a healthy body should have brought glucose almost all the way back down to its fasting level; a reading that's still raised at three hours often signals a slower glucose clearance than the earlier hours alone would suggest. This timepoint doesn't appear in the shorter 75-gram or 50-gram protocols, so it's specific to the older, four-draw gestational diabetes test.
This is the fourth and final plasma glucose reading, in mg/dL, in the 100-gram gestational diabetes protocol, taken three hours after the glucose drink, following the fasting, one-hour, and two-hour samples. Because it comes so long after the drink, this reading is compared against a lower cutoff than the earlier hours, reflecting how far glucose should have fallen by this point in a healthy response.
This reading only exists because of the older, two-step approach to gestational diabetes screening, where a 100-gram glucose drink is followed by blood draws at one, two, and three hours, on top of the initial fasting sample. Using the Carpenter-Coustan criteria, a three-hour reading of 140 mg/dL or higher is one of four values checked; if two or more of the four — fasting, one-hour, two-hour, or three-hour — are abnormal, gestational diabetes is confirmed.
Because the fasting, one-hour, and two-hour draws already give a good picture of the glucose peak and early clearance, the three-hour reading mainly catches a slower tail — cases where glucose is coming down but more gradually than expected. On its own, a single abnormal three-hour value with the other three normal usually isn't enough for a diagnosis, though your doctor may watch it more closely or repeat the test later in pregnancy.
This is normally the last sample of the visit, so once it's taken you can eat again and resume your normal routine.
Using the Carpenter-Coustan criteria, a three-hour reading below 140 mg/dL is considered normal. Ranges can vary slightly by lab, so check the figure printed on your own report.
The 75-gram, one-step protocol only checks fasting, one-hour, and two-hour values. The three-hour draw is specific to the older, 100-gram, two-step protocol, which is a longer four-point test.
No. Under Carpenter-Coustan criteria, at least two of the four values — fasting, one-hour, two-hour, or three-hour — need to be abnormal for a diagnosis.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Yes. This is normally the last blood draw of the test, so you can eat, drink, and resume your usual activities once it's done.
It points to slower clearance further along the curve. Glucose that's still coming down at three hours more gradually than a healthy response would show, rather than the size of the initial rise or peak.
That depends on your specific results and your doctor's judgement. A single borderline value sometimes leads to closer monitoring or a repeat test later in pregnancy rather than an automatic diagnosis.