Pregnancy Lab Tests
Glucose Tolerance Test (OGTT) for Gestational Diabetes
Screens for gestational diabetes — among the most common pregnancy complications in India
What does it measure?
The Oral Glucose Tolerance Test (OGTT) measures how your body handles a standard sugar load. You drink a glucose solution and your blood sugar is measured at set intervals. The test identifies Gestational Diabetes Mellitus (GDM) — high blood sugar that develops during pregnancy in women who did not have diabetes before. GDM occurs because pregnancy hormones (especially human placental lactogen) cause insulin resistance, and some women's pancreas cannot compensate sufficiently. India uses two main methods: the DIPSI method and the WHO/IADPSG criteria.
When is it ordered?
Routinely at 24–28 weeks for all pregnant women. Done earlier — in the first trimester or as soon as possible — if risk factors are present: BMI greater than 25 kg/m², family history of Type 2 diabetes, personal history of GDM in a previous pregnancy, PCOS (polycystic ovarian syndrome), previous baby weighing more than 4kg at birth, previous unexplained stillbirth, or glycosuria (glucose in urine) at routine check.
Normal ranges in pregnancy
What does an abnormal result mean?
GDM means your blood sugar is higher than normal during pregnancy. This causes the baby to receive excess glucose through the placenta, leading to macrosomia (large baby, EFW > 90th percentile) — increasing the risk of obstructed labour, shoulder dystocia, and emergency C-section. After birth, the baby's own insulin production (stimulated by the high glucose it received) can cause neonatal hypoglycaemia (dangerously low blood sugar in the newborn) requiring special monitoring. For the mother, GDM significantly increases the lifetime risk of developing Type 2 diabetes — about 50% of women with GDM develop T2DM within 10 years. GDM itself, once diagnosed, is managed with medical nutrition therapy (diet changes) and, if needed, metformin or insulin — and most women achieve excellent control.
What this means for South Indian women
India has one of the highest rates of GDM in the world — estimates range from 15–25% in urban South India, compared to the global average of around 14%. South Indian dietary patterns (white rice as the staple, refined carbohydrates, limited protein, and sweets) contribute to this elevated risk. The genetic predisposition to insulin resistance is also higher in South Asians. The good news: GDM is very manageable. Dietary changes — switching to millets (ragi, jowar, bajra), reducing white rice portion sizes, increasing protein at each meal, reducing sugary drinks — can normalise blood sugar in many women without medication. Physical activity (30 minutes of walking daily) is also proven to improve insulin sensitivity.
Frequently asked questions
What is the difference between the DIPSI test and the standard OGTT?
The DIPSI (Diabetes in Pregnancy Study group India) method is a simplified, non-fasting single-point test: you arrive without fasting, drink 75g of glucose in water, and give one blood sample at 2 hours. A result ≥ 140 mg/dL diagnoses GDM. It is practical for busy antenatal clinics. The WHO/IADPSG OGTT requires overnight fasting and three blood samples (fasting, 1-hour, 2-hour). Both are valid — your doctor will choose based on your clinic's protocol.
Do I need to fast before the glucose test?
It depends on which method your clinic uses. For the DIPSI method: no fasting required. For the WHO OGTT: yes — you must fast for 8–10 hours (usually overnight) before the test. Ask your doctor or the laboratory specifically which test they are using and whether to fast.
My GDM test was positive. What happens now?
A positive OGTT means GDM is diagnosed. You will be referred to a dietitian or given a medical nutrition therapy (MNT) plan — the cornerstone of GDM management. Blood sugar monitoring at home (fasting and post-meal) is started. If diet alone does not achieve target blood sugars within 1–2 weeks, medication (usually metformin or insulin) is added. GDM requires more frequent antenatal visits, fetal growth scans, and careful delivery planning.
Does gestational diabetes mean I will have diabetes forever?
GDM usually resolves after delivery — blood sugar typically returns to normal within 6 weeks postpartum. However, it is a strong warning signal: women with GDM have a 50% lifetime risk of developing Type 2 diabetes. A fasting blood sugar or HbA1c is recommended at 6 weeks postpartum to confirm resolution, and annual screening thereafter. Lifestyle changes (healthy weight, regular exercise, reduced refined carbohydrates) significantly reduce the conversion to T2DM.
Does one abnormal value mean I have GDM?
Yes. According to the current DIPSI and International guidelines, even a single value meeting or exceeding the threshold is enough to diagnose Gestational Diabetes. Early diagnosis is key to a healthy outcome.
Is insulin safe during pregnancy?
Yes. Insulin is the safest medication for controlling blood sugar in pregnancy. It does not cross the placenta and has been used safely in pregnant women for decades. If your doctor recommends insulin, it means your blood sugars need tighter control than diet and oral medications can achieve. Starting insulin is not a sign of failure — it is the right treatment to protect your baby.