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Gestational diabetes
Gestational diabetes comes from insulin resistance produced by the placenta in the second half of pregnancy; it is found at 24–28 weeks, treated first with diet and exercise and then with insulin, and the main risk is a large baby with shoulder dystocia and neonatal hypoglycaemia.
Why it matters in the exam
In Israel two-step screening is usual: a 50 g glucose challenge at 24–28 weeks, and if the result is 140 mg/dL or more, a 100 g tolerance test with four measurements, with the diagnosis made when two or more values are abnormal. Questions test the cut-offs, the difference between gestational and pre-existing diabetes, and drug treatment: insulin is first line, and metformin is an alternative that crosses the placenta. The other approach is the one-step method: a 75 g tolerance test, where a single abnormal value is enough.
Keep the distinction clear: diabetes that existed before pregnancy raises the risk of congenital anomalies (cardiac defects, caudal regression), so control before conception and a low HbA1c are the goal; gestational diabetes does not cause anomalies, but causes macrosomia, polyhydramnios, preeclampsia and neonatal hypoglycaemia. After delivery glucose usually returns to normal, but the lifetime risk of type 2 diabetes is very high, so a 75 g tolerance test is done 4–12 weeks after birth with follow-up every 1–3 years.
Key points
- Screening at 24–28 weeks; 50 g challenge with a cut-off of 140.
- Diagnosis: 2 abnormal values on the 100 g test or one value on the 75 g test.
- Treatment: diet and exercise, and insulin if not at target.
- Complications: macrosomia, shoulder dystocia, neonatal hypoglycaemia, preeclampsia.
- After delivery: a 75 g test 4–12 weeks postpartum and lifelong follow-up.
Summary table
| Step | Cut-offs | Interpretation | Exam notes |
|---|---|---|---|
| Screening (50 g, non-fasting) | One hour: 140 mg/dL or more | Positive → 100 g test | 24–28 weeks; earlier with risk factors |
| 100 g test (Carpenter–Coustan) | Fasting 95, 1 hour 180, 2 hours 155, 3 hours 140 | 2 or more abnormal values = gestational diabetes | One abnormal value → surveillance and sometimes a repeat |
| 75 g test (one-step) | Fasting 92, 1 hour 180, 2 hours 153 | One abnormal value is enough | Diagnoses more women |
| Overt diabetes in pregnancy | Fasting 126 or more or HbA1c 6.5% or more at the first visit | Pre-existing diabetes | Risk of anomalies; managed like pre-existing diabetes |
| Treatment targets | Fasting below 95; 1 hour after a meal below 140; 2 hours below 120 | Not at target after 1–2 weeks of diet → medication | Insulin first line; metformin an alternative |
A free exam question
אישה ללא סוכרת, בשבוע 32 . רמות גלוקוז בצום תקינות, אך לאחר ארוחה יש עלייה חדה בגלוקוז. מהו המנגנון העיקרי היכול להסביר ממצא זה? (the question as examined, in Hebrew)
- א. ירידה בהפרשת אינסולין
- ב. ירידה בפינוי גלוקוז כלייתי
- ג. תנגודת לאינסולין מתווכת הורמוני שלייה
- ד. ירידה ברגישות לקורטיזול
Example question from the licensing exam (IMLE)
A 25 weeks pregnant 30-year-old woman has a glucose challenge test (GCT) result of glucose 203mg/dl. Which of the following is the next step in managing this patient?
- A. Routine follow up
- B. Repeat GCT at 28 weeks of gestation
- C. Oral glucose tolerance test (OGTT)
- D. Initiating treatment for gestational diabetes
- E. Initiate treatment with insulin pump
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Sources
- ACOG Practice Bulletin No. 190, 2018 — Gestational Diabetes Mellitus
- American Diabetes Association Standards of Care, 2025 — Management of Diabetes in Pregnancy
- IADPSG recommendations, 2010 — Diagnosis and classification of hyperglycemia in pregnancy
- Williams Obstetrics, 26th edition (2022) — Diabetes Mellitus
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.