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Glucose Test in Pregnancy — OGTT, Procedure & Values

What the glucose test between weeks 24 and 28 screens for, how it works — and what an abnormal result really means.

Evidence-basedUpdated: April 2026
Table of Contents

What is the pregnancy glucose test?

The glucose test — technically the OGTT (oral glucose tolerance test) — is a routine screening between weeks 24 and 28 of pregnancy. It checks whether your body produces enough insulin during pregnancy to lower blood sugar again after a defined amount of sugar. The goal is early detection of gestational diabetes (GDM) — a form of diabetes that only develops during pregnancy and usually disappears after birth.

Why test at all?

In pregnancy, the placenta produces hormones that weaken insulin's effect — a biologically useful adaptation so the baby is reliably supplied with energy. Sometimes the pancreas cannot produce enough insulin to compensate. Blood sugar rises, and the baby reacts: too much sugar in maternal blood means too much sugar supply for the baby. Untreated gestational diabetes increases the risk of a large-for-date baby, birth complications, preterm birth, and later metabolic problems.

In Germany the glucose test is part of the recommended maternity guideline screenings and is covered by statutory health insurance. The S3 guideline on gestational diabetes from the German Society of Gynaecology and Obstetrics (DGGG) recommends a two-step procedure (50 g screening test plus 75 g OGTT if needed) — internationally (WHO, ACOG) the one-step 75 g test is often used directly. Both approaches are evidence-based.

When is the glucose test performed?

The standard window is weeks 24+0 to 27+6 of pregnancy. In this phase impaired glucose tolerance shows up most reliably, because placental hormones are at full effect. With risk factors, the test can be done earlier — even in the first trimester.

Early testing with risk factors

  • Pre-pregnancy BMI ≥ 30 kg/m²
  • Age ≥ 35 years
  • Gestational diabetes in a previous pregnancy
  • Macrosomic baby in a previous pregnancy (≥ 4500 g)
  • Type 2 diabetes in the family (parents, siblings)
  • Polycystic ovary syndrome (PCOS)
  • History of recurrent miscarriage or stillbirth
  • Origin from regions with high diabetes prevalence

If one or more of these factors apply to you, your gynaecologist will probably arrange the glucose test already in early pregnancy. A normal early test is repeated later — as for all pregnant women — between weeks 24 and 28.

How the glucose test works — step by step

In Germany a two-step approach is usually used: first a pre-test with 50 g glucose (non-fasting), and only if this is abnormal the actual 75 g fasting OGTT follows. In many other countries the 75 g test is performed directly. Your gynaecologist will tell you which applies to you.

Step 1 — 50 g screening test (pre-test)

  1. You do not need to fast — you may eat normally beforehand.
  2. In the practice you drink a solution with 50 g glucose in about 200 ml water within 5 minutes.
  3. Exactly 60 minutes later blood is drawn and blood sugar measured.
  4. A value below 135 mg/dl (7.5 mmol/l) is unremarkable — the test is then complete.
  5. A value ≥ 135 mg/dl is abnormal: the 75 g OGTT follows for clarification.
  6. A value ≥ 200 mg/dl already counts as overt gestational diabetes — no further test needed.

Step 2 — 75 g OGTT (fasting test)

  1. Eat normally the evening before, then fast at least 8 (max 14) hours — water only.
  2. No smoking, no strenuous exercise in the morning.
  3. In the practice: first blood draw fasting.
  4. Then drink 75 g glucose in 300 ml water within 3-5 minutes — often very sweet and unpleasant.
  5. After 60 minutes: second blood draw.
  6. After 120 minutes: third blood draw.
  7. Between draws: sit quietly, don't eat, don't drink (except a little water), don't walk around.

Plan about 2.5 hours and bring something to read. Afterwards you can eat normally — many women feel hungry briefly or have a small blood sugar dip after the test. Eat something with protein and complex carbs before driving.

Understanding values — DGGG cut-offs at a glance

The DGGG S3 guideline defines clear cut-off values for the 75 g OGTT. Important: a single exceeded value is enough for a diagnosis of gestational diabetes — not all three values have to be abnormal.

Cut-offs 75 g OGTT (DGGG, ADA, WHO)

Fasting value

  • Normal: < 92 mg/dl (5.1 mmol/l)
  • Abnormal: ≥ 92 mg/dl

1-hour value

  • Normal: < 180 mg/dl (10.0 mmol/l)
  • Abnormal: ≥ 180 mg/dl

2-hour value

  • Normal: < 153 mg/dl (8.5 mmol/l)
  • Abnormal: ≥ 153 mg/dl

Normal result — what does it mean?

All three values below the cut-offs — congratulations, no gestational diabetes. A balanced diet, regular movement, and moderate weight gain during pregnancy still make sense. With risk factors or later ultrasound findings (large-for-date baby, polyhydramnios), the test may be repeated.

One or more values abnormal

A single exceeded value is enough to diagnose gestational diabetes. It sounds scary at first but is very treatable. About 85-90 % of all women with gestational diabetes manage well with dietary changes and exercise; only a minority need insulin. What matters now: stay calm, make an appointment with a diabetologist or specialised practice, learn self-monitoring of blood sugar.

What happens if the test is abnormal?

Take a breath first. A diagnosis of gestational diabetes is not a catastrophe — it means more attentive care and more conscious nutrition and movement in the remaining weeks. Your baby gets the best possible start because of this. What follows is organised in three stages.

The three treatment stages

  1. Stage 1 — Education, dietary change, and moderate exercise (30 min brisk walk daily or swimming). Self-monitoring of blood sugar 4× daily (fasting + 1 h after main meals).
  2. Stage 2 — If targets are not reached despite diet after 1-2 weeks: basal insulin at night and/or meal-time insulin. Insulin is neutral regarding placental transfer, well-established, and safe for baby.
  3. Stage 3 — Close monitoring: ultrasound every 3-4 weeks (growth, amniotic fluid), CTG from about week 32, delivery planning in a clinic with neonatology.

False positives and common worries

The OGTT is a good but not perfect test. Several factors can lead to falsely elevated values — and should be known so you don't worry unnecessarily or start therapy on a shaky basis.

Typical sources of error

  • Not actually fasting (e.g. coffee with milk, sweet, chewing gum)
  • Acute infection, fever, or stress on test day
  • Low-carbohydrate diet in the days before (body is 'deconditioned')
  • Taking corticosteroids or beta-mimetics (e.g. for threatened preterm birth)
  • Vomiting after the glucose drink — test must be repeated
  • Very short or very long fasting period
  • Physical activity between blood draws

If you're unsure whether the test was carried out correctly, talk to your gynaecologist. A repeat test under clean conditions is often wiser than therapy based on suspicion.

Myths about the glucose test

Myth 1: 'I can starve myself thin before the test'

Wrong. Eating almost no carbs for days can paradoxically cause higher values on test day — the metabolism overshoots. Eat normally and carb-rich in the 3 days before the test (at least 150 g/day).

Myth 2: 'I can refuse the test, it's voluntary'

Technically correct — every test is voluntary. But: gestational diabetes often runs without symptoms. Without the test it frequently goes undetected — with consequences for you and your baby. If you're sceptical, talk openly with your doctor about your concerns. There are usually good answers to worries about the test.

Myth 3: 'I'm slim — I don't need the test'

Wrong. Gestational diabetes also affects slim women — especially with family history, PCOS, or certain geographic backgrounds. BMI is only one of many risk factors. Diagnosis is independent of whether you're 'fat' or 'thin'.

Frequently Asked Questions

Do I really not need to fast for the 50 g screening test?
Correct. The 50 g screening test is explicitly designed to be independent of the last meal. You can eat a normal breakfast and come to the practice during the day. The actual 75 g OGTT, however, must be strictly fasting — at least 8, maximum 14 hours.
Is the glucose test covered by health insurance?
Yes. In Germany, the 50 g screening test and — if abnormal — the 75 g OGTT are part of the maternity guidelines and covered by statutory health insurance. Private insurers usually reimburse as well. In high-risk patients an early test is also covered.
The sweet drink makes me nauseous — what can I do?
Drink the solution cold (tastes less intrusive), smell a lemon slice in between, drink slowly in small sips — but finish within 5 minutes. If you vomit, the test must be repeated another day. In individual cases a standardised breakfast with a blood sugar profile can be an alternative — discuss with your doctor.
I had gestational diabetes in my last pregnancy. Will I get it again?
Recurrence risk is 30-50 %. Therefore you'll be offered an early test already in the first trimester and, if normal, the regular test at weeks 24-28. Healthy diet, movement, and moderate weight gain lower the risk. Long-term, women with gestational diabetes have an increased risk of type 2 diabetes — regular post-partum check-ups matter.
Can I do the test at home with my own blood sugar meter?
No. Diagnosis requires a venous blood draw from the arm with laboratory analysis. Capillary meters (finger prick) have too much measurement uncertainty and are not approved for diagnosis. For self-monitoring after diagnosis, however, they are standard.
What does a fasting value of 90 mg/dl mean — borderline?
90 mg/dl is just below the cut-off of 92 mg/dl and formally counts as normal. However, in pregnancy even 'upper normal range' is relevant. Many doctors already give concrete dietary advice at values ≥ 85 mg/dl and monitor baby growth more closely. An HbA1c or a repeat measurement can be sensible.
Can I postpone the test to week 30 because of my morning sickness?
A short postponement by 1-2 weeks is usually unproblematic and wiser than doing the test with acute nausea. But the test shouldn't be done later than week 30, because then there's not enough time for dietary adjustment and possible therapy. Discuss with your doctor.
Does the glucose drink have harmful effects on my baby?
No. 50 or 75 g of glucose given once is harmless for your baby. There is no robust evidence of fetal harm from the glucose drink. The briefly elevated maternal blood sugar leads to a short insulin response — nothing more.
What's the difference between HbA1c and OGTT?
HbA1c (long-term sugar) reflects average blood sugar of the past 8-12 weeks and is mainly suitable for diagnosing pre-existing diabetes. For diagnosing gestational diabetes it's not suitable — the DGGG recommends the OGTT. HbA1c is used as a supplement, e.g. for assessment at the start of pregnancy.
What happens to gestational diabetes after birth?
With delivery of the placenta the diabetogenic hormones disappear, and in most women blood sugar normalises within a few days. Guidelines recommend a repeat 75 g OGTT 6-12 weeks after birth — to rule out persistence. Afterwards, check-ups every 1-3 years, because the risk of later type 2 diabetes is increased.
Can I have a healthy birth with gestational diabetes?
Absolutely. With well-controlled blood sugar values the prognosis is very good. A vaginal birth is generally possible, provided the baby hasn't grown too large (estimated birth weight > 4500 g can be a reason for a planned caesarean). Delivery should take place in a clinic with neonatology, because newborns after GDM need close blood sugar monitoring in the first hours.

References

Our content draws on publicly available guidelines from recognised medical institutions.

  1. [1]Deutsche Gesellschaft für Gynäkologie und Geburtshilfe. S3-Leitlinie Gestationsdiabetes mellitus (GDM). 2018. https://www.awmf.org/leitlinien/detail/ll/057-008.html
  2. [2]World Health Organization. WHO recommendations on antenatal care for a positive pregnancy experience. 2016. https://www.who.int/publications/i/item/9789241549912
  3. [3]American College of Obstetricians and Gynecologists. Nutrition During Pregnancy — FAQ. 2023. https://www.acog.org/womens-health/faqs/nutrition-during-pregnancy
  4. [4]Bundeszentrale für gesundheitliche Aufklärung. familienplanung.de — Schwangerschaft. 2024. https://www.familienplanung.de/schwangerschaft/

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This guide is for general information only and does not replace medical advice. The glucose test and interpretation of your values always belong in the hands of your gynaecologist or diabetologist. For questions about your specific values, procedure, or therapy, contact your care provider.