The glucose test, and the trial that changed how to read it
Two approaches. One diagnoses twice as many women. Neither improved outcomes.
There are two ways to test for gestational diabetes. The two-step approach starts with a 50 gram drink and a single blood sample, and only proceeds to a longer test if that is abnormal. The one-step approach goes straight to a 75 gram fasting test.
A pragmatic randomized trial of 23,792 women compared them directly:
| Outcome | One-step | Two-step |
|---|---|---|
| Diagnosed with gestational diabetes | 16.5% | 8.5% |
| Large-for-gestational-age baby | 8.9% | 9.2% |
| Serious perinatal outcome | 3.1% | 3.0% |
| Gestational hypertension or preeclampsia | 13.6% | 13.5% |
| First cesarean | 24.0% | 24.6% |
The one-step approach nearly doubled the number of women given a diagnosis, and changed nothing measurable about outcomes. Only 66% of women completed the one-step test, against 92% for two-step.
What this does not meanIt does not mean gestational diabetes is unimportant. It means the extra women diagnosed by the wider net did not measurably benefit from being diagnosed. Which test your practice uses is a reasonable thing to ask about.
Where this comes from:
158. Hillier TA, Pedula KL, Ogasawara KK, Vesco KK, Oshiro CES, Lubarsky SL, et al. A pragmatic, randomized clinical trial of gestational diabetes screening. N Engl J Med. 2021;384(10):895-904.
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