# Situation: The nurse works in the high-risk pregnancy unit of a provincial hospital that receives referred pregnant clients from rural health units (RHUs). A 30-year-old gravida 2, para 1, at 26 weeks' gestation has a one-step 75-g oral glucose tolerance test (OGTT). Results: fasting 88 mg/dL (4.9 mmol/L); 1 hour 176 mg/dL (9.8 mmol/L); 2 hours 158 mg/dL (8.8 mmol/L). The hospital uses the International Association of Diabetes and Pregnancy Study Groups (IADPSG) criteria. How should the nurse interpret these results?

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> subject: Nursing Practice II — Maternal and Child Health Nursing

## 문제

Situation: The nurse works in the high-risk pregnancy unit of a provincial hospital that receives referred pregnant clients from rural health units (RHUs).

A 30-year-old gravida 2, para 1, at 26 weeks' gestation has a one-step 75-g oral glucose tolerance test (OGTT). Results: fasting 88 mg/dL (4.9 mmol/L); 1 hour 176 mg/dL (9.8 mmol/L); 2 hours 158 mg/dL (8.8 mmol/L). The hospital uses the International Association of Diabetes and Pregnancy Study Groups (IADPSG) criteria. How should the nurse interpret these results?

## 보기

1. Normal, because the fasting and 1-hour values are below their thresholds
2. Borderline, so a 100-g 3-hour test is needed to confirm the diagnosis
3. Not diagnostic, because at least two values must reach the thresholds
4. Gestational diabetes, because the 2-hour value reaches its threshold **✔ 정답**

**정답: 4**

## 해설

With the one-step 75-g OGTT, gestational diabetes is diagnosed when any ONE value meets or exceeds the threshold: fasting 92 mg/dL (5.1 mmol/L), 1 hour 180 mg/dL (10.0 mmol/L), or 2 hours 153 mg/dL (8.5 mmol/L). Her 2-hour value of 158 mg/dL (8.8 mmol/L) exceeds 153 mg/dL, so she has gestational diabetes even though the other two values are normal. The two-abnormal-values rule belongs to the 100-g 3-hour test of the two-step approach.

## 심화 해설

Interpretation of the 75-g OGTT using IADPSG criteria

The one-step 75-g oral glucose tolerance test (OGTT) is interpreted using the International Association of Diabetes and Pregnancy Study Groups (IADPSG) thresholds. The key principle is that gestational diabetes mellitus (GDM) is diagnosed when any single plasma glucose value meets or exceeds its threshold—not when two or more values are abnormal. The IADPSG diagnostic cutoffs for the 75-g test are: fasting 92 mg/dL (5.1 mmol/L), 1-hour 180 mg/dL (10.0 mmol/L), and 2-hour 153 mg/dL (8.5 mmol/L).

For this client, the fasting value of 88 mg/dL (4.9 mmol/L) is below the fasting threshold, and the 1-hour value of 176 mg/dL (9.8 mmol/L) is below the 1-hour threshold. However, the 2-hour value of 158 mg/dL (8.8 mmol/L) exceeds the 2-hour threshold of 153 mg/dL (8.5 mmol/L). Because only one elevated value is required for diagnosis under the one-step IADPSG approach, this client has gestational diabetes.

Watch out! The rule requiring two or more abnormal values belongs to the two-step approach, which uses a 100-g, 3-hour OGTT after an initial 50-g glucose challenge. In that protocol, the diagnostic thresholds are higher (fasting 95 mg/dL, 1-hour 180 mg/dL, 2-hour 155 mg/dL, 3-hour 140 mg/dL), and at least two values must be elevated. Confusing the two-step rule with the one-step 75-g test is a common error.

The rationale for using a single elevated value in the one-step approach is grounded in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study data, which demonstrated a continuous, linear relationship between maternal glucose levels and adverse perinatal outcomes—including large-for-gestational-age infants, neonatal hypoglycemia, and cesarean delivery. The IADPSG thresholds were selected to identify pregnancies at meaningfully increased risk, and requiring two abnormal values would miss a substantial proportion of affected pregnancies. The NIH consensus conference noted that the one-step approach diagnoses GDM in approximately 15–18% of pregnancies, whereas the two-step approach yields lower rates, reflecting the different diagnostic philosophies rather than a difference in underlying risk.

A comparison of the two testing strategies clarifies why the interpretation differs:

| Feature | One-step 75-g OGTT (IADPSG) | Two-step 100-g OGTT (Carpenter-Coustan) |
| --- | --- | --- |
| Initial step | None; proceed directly to 75-g OGTT after overnight fast | 50-g glucose challenge (non-fasting), then 100-g OGTT if screen positive |
| Diagnostic rule | Any ONE value at or above threshold | TWO or more values at or above threshold |
| Fasting threshold | 92 mg/dL (5.1 mmol/L) | 95 mg/dL (5.3 mmol/L) |
| 1-hour threshold | 180 mg/dL (10.0 mmol/L) | 180 mg/dL (10.0 mmol/L) |
| 2-hour threshold | 153 mg/dL (8.5 mmol/L) | 155 mg/dL (8.6 mmol/L) |
| 3-hour threshold | Not applicable | 140 mg/dL (7.8 mmol/L) |

Key point! The one-step IADPSG approach is more sensitive because it captures glucose intolerance at any single time point. A client with an isolated elevated 2-hour value—as in this case—would be missed by the two-step rule but is correctly identified as having GDM under IADPSG criteria. This has direct implications for nursing care: the client requires immediate referral for medical nutrition therapy, blood glucose self-monitoring, and fetal surveillance, rather than a repeat confirmatory test.

The study comparing 75-g and 100-g OGTTs using IADPSG thresholds found that the 75-g test identified GDM based on single-value criteria, with the 2-hour value frequently contributing to the diagnosis. This supports the clinical observation that post-load hyperglycemia is a common and clinically significant pattern in GDM. The higher diagnostic yield of the one-step approach also means that nurses in high-risk pregnancy units will encounter more clients requiring education on glucose monitoring, dietary modification, and the potential need for insulin therapy when glycemic targets are not met with lifestyle intervention alone.

## 임상 시나리오

One-Step 75-g OGTT InterpretationIADPSG criteria for gestational diabetes
Diagnose gestational diabetes when any single value meets or exceeds threshold: fasting 92 mg/dL, 1-hour 180 mg/dL, or 2-hour 153 mg/dL.

This client's 2-hour value of 158 mg/dL exceeds 153 mg/dL, so she has gestational diabetes even though fasting and 1-hour values are normal.

CautionDo not apply the two-abnormal-values rule; that belongs to the 100-g 3-hour test in the two-step approach.

## 핵심 개념

- **IADPSG criteria** — International Association of Diabetes and Pregnancy Study Groups thresholds for 75-g OGTT: fasting 92, 1-h 180, 2-h 153 mg/dL
- **One-step 75-g OGTT** — Screening and diagnostic test where any single elevated glucose value diagnoses gestational diabetes
- **Two-step approach** — 50-g challenge followed by 100-g 3-hour OGTT; requires two abnormal values for diagnosis
- **Gestational diabetes mellitus** — Glucose intolerance first recognized during pregnancy, diagnosed by OGTT thresholds

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