**Core Concept**
Glucose Tolerance Test (GTT) is a diagnostic tool to assess carbohydrate metabolism in pregnant women. In pregnancy, GTT is used to screen for gestational diabetes mellitus (GDM), a condition characterized by high blood glucose levels that can have serious consequences for both mother and fetus.

**Why the Correct Answer is Right**
The American College of Obstetricians and Gynecologists (ACOG) recommends performing a 50g glucose challenge test (GCT) in pregnant women at 24-28 weeks of gestation. If the blood glucose level is above 95mg/100ml (or 5.3mmol/L), it indicates an abnormal glucose tolerance and warrants further evaluation with a 100g oral glucose tolerance test (OGTT). This threshold is chosen because it has a high sensitivity for detecting GDM, which is associated with increased risks of maternal and fetal complications.

**Why Each Wrong Option is Incorrect**
**Option A:** 80gm/100ml is too low to be an accurate threshold for diagnosing GDM, as it would lead to false positives and unnecessary further testing.

**Option B:** 85gm/100ml is still below the recommended threshold, and using this value would result in missed cases of GDM.

**Option C:** 90gm/100ml is close to the correct threshold but is still too low, as it would not capture all women with impaired glucose tolerance.

**Clinical Pearl / High-Yield Fact**
Remember that the 50g glucose challenge test is a screening tool, not a diagnostic test. Women who screen positive (i.e., above 95mg/100ml) should undergo a 100g OGTT to confirm the diagnosis of GDM.

**✓ Correct Answer: D. 95gm/100ml**