Calculator Form
Use mg/dL for all glucose values. Leave unrelated fields blank.
Formula Used
This calculator combines testing thresholds with an optional background risk score. The score helps prioritize follow-up but does not diagnose gestational diabetes on its own.
| Pathway | Rule | Threshold Logic |
|---|---|---|
| One-step 75 g OGTT | IADPSG style cutoffs | Positive when any entered value meets or exceeds fasting 92, 1 hour 180, or 2 hour 153 mg/dL. |
| Two-step 50 g screen | User-selected screen cutoff | Positive when the 1 hour challenge meets or exceeds 130, 135, or 140 mg/dL. |
| Two-step 100 g OGTT | Carpenter-Coustan | Counts abnormal values at fasting 95, 1 hour 180, 2 hour 155, and 3 hour 140 mg/dL. Two or more abnormal values flag the pathway. |
| Two-step 100 g OGTT | NDDG | Counts abnormal values at fasting 105, 1 hour 190, 2 hour 165, and 3 hour 145 mg/dL. Two or more abnormal values flag the pathway. |
Risk score formula: age points + BMI points + previous gestational diabetes + prior macrosomia + family history + PCOS + hypertension + glycosuria.
Risk bands: Low = 0 to 2 points, Moderate = 3 to 5 points, High = 6 or more points.
How to Use This Calculator
- Select either the one-step or two-step testing pathway.
- Enter gestational age, maternal age, and pre-pregnancy BMI if available.
- For the two-step pathway, choose your 50 g screen cutoff and 100 g rule.
- Type the glucose values from your lab report using mg/dL units.
- Add optional risk factors for a broader pregnancy risk profile.
- Press the calculate button to display the result above the form.
- Use the CSV or PDF buttons to save the interpretation.
- Review the output with your clinician for final medical guidance.
Example Data Table
| Scenario | Pathway | Key Values | Interpretation |
|---|---|---|---|
| Example 1 | One-step 75 g | Fasting 94, 1 h 182, 2 h 149 | Positive because fasting and 1 hour cross common one-step thresholds. |
| Example 2 | One-step 75 g | Fasting 86, 1 h 166, 2 h 134 | Negative because none of the three entered values reach the thresholds. |
| Example 3 | Two-step 50 g + 100 g | 50 g screen 156, fasting 98, 1 h 184, 2 h 150, 3 h 132 | Positive under Carpenter-Coustan because two diagnostic values are abnormal. |
| Example 4 | Two-step 50 g + 100 g | 50 g screen 128, no OGTT entered | Negative screen at a 140 mg/dL cutoff, pending clinician context. |
FAQs
1. When is gestational diabetes screening usually done?
Most routine screening happens between 24 and 28 weeks of pregnancy. Earlier testing may be used when risk factors are already present.
2. What is the difference between one-step and two-step testing?
The one-step pathway uses a 75 g oral glucose tolerance test. The two-step pathway starts with a 50 g screen, then uses a 100 g diagnostic test if needed.
3. Why can I choose different 50 g screen cutoffs?
Some clinics use 130, 135, or 140 mg/dL for the 50 g challenge. The calculator lets you match the cutoff used by your testing center.
4. Can one abnormal value diagnose gestational diabetes?
Under common one-step 75 g criteria, one abnormal value can flag the pathway. Under common two-step 100 g rules, at least two abnormal values are usually required.
5. Why does this calculator include risk factors?
Risk factors help show whether extra follow-up may be reasonable. They add context, but they do not replace formal laboratory interpretation or diagnosis.
6. Can I enter mmol/L values?
This version expects mg/dL values. Convert your report first if your laboratory uses mmol/L, otherwise the interpretation will be inaccurate.
7. What if my test happened outside 24 to 28 weeks?
The calculator still works, but it adds a note. Screening timing can vary for high-risk pregnancies or delayed prenatal care.
8. Is this calculator a medical diagnosis?
No. It is an educational screening aid that summarizes entered values against common thresholds. Final interpretation belongs to your obstetric clinician.