Gestational Diabetes Mellitus — Screening (DIPSI, IADPSG), Management and Follow-up

Gestational diabetes mellitus (GDM) is hyperglycaemia that is diagnosed or develops during pregnancy. It is divided into class A1GDM (controlled by diet) and class A2GDM (needs drugs). It matters for two reasons: treatment during pregnancy reduces adverse outcomes, and women who have had GDM carry a high long-term risk of type 2 diabetes.

Normal pregnancy is a state of rising insulin resistance. Placental hormones — growth hormone, corticotrophin-releasing hormone, human placental lactogen (hPL), prolactin, oestrogen and progesterone — all oppose insulin, and hPL is the main one. In most women the pancreas compensates with more insulin secretion and beta-cell growth. GDM appears when that compensation fails, which is why it typically surfaces in the second half of pregnancy and why the classic screening window is 24–28 weeks.

• Strongest risk factors: family history of diabetes, previous GDM, South or Southeast Asian ethnicity, higher parity and high BMI.
• Others: physical inactivity, hypertension, polycystic ovary syndrome, low HDL or high triglycerides, a previous large baby.
• Why universal screening in India: Indian women develop GDM at high rates and often early — the national guideline notes that about one-third of GDM is already detectable in the first trimester.

The Ministry of Health and Family Welfare's 2018 technical and operational guidelines endorse a single-step test — the non-fasting 75 g approach used by the Diabetes in Pregnancy Study Group India (DIPSI). One visit both screens and diagnoses — no fasting, no second appointment.

1. Give 75 g of glucose dissolved in about 300 ml of water, whether the woman is fasting or not, irrespective of her last meal. She should finish it within 5–10 minutes.
2. Measure blood glucose 2 hours later with a plasma-calibrated glucometer (or a laboratory analyser where available).
3. 2-hour value ≥140 mg/dL = GDM. Below 140 mg/dL is normal.
4. If she vomits within 30 minutes, repeat the test the next day; after 30 minutes, the test continues.

Internationally, the International Association of the Diabetes and Pregnancy Study Groups (IADPSG) proposed a one-step fasting 75 g OGTT in 2010; WHO adopted the same thresholds in 2013, and the American Diabetes Association uses them for its one-step strategy. A single abnormal value is enough.

The trade-off is practical. The fasting OGTT needs an overnight fast and a 2-hour wait in clinic; DIPSI works with whatever the woman last ate and a glucometer, which is why India chose it for programme use at primary health centres. Using IADPSG/WHO 2013 criteria consistently diagnoses more women than older thresholds, so prevalence figures depend heavily on which test was used.

The national guideline uses a stepwise plan that starts the day GDM is diagnosed.

1. Medical nutrition therapy (MNT) + exercise for 2 weeks. A carbohydrate-controlled, balanced meal plan, and walking or exercising for 30 minutes a day.
2. Check 2-hour post-prandial blood sugar (PPBS) after 2 weeks.
3. PPBS <120 mg/dL: continue MNT and exercise; repeat testing as per the high-risk pregnancy protocol (at least monthly in the second and third trimesters).
4. PPBS ≥120 mg/dL: start metformin or insulin on top of MNT.

The classic chain is the Pedersen hypothesis: maternal glucose crosses the placenta, the fetal pancreas answers with hyperinsulinaemia, and fetal insulin's anabolic effect drives growth — macrosomia is a birth weight of 4,000 g or more. After the cord is cut the glucose supply stops while fetal insulin stays high, causing neonatal hypoglycaemia. Macrosomic babies are at risk of shoulder dystocia, clavicle fractures and brachial plexus injury — see Erb's palsy. GDM pregnancies also show delayed fetal lung maturity, which is why these babies have more respiratory distress and why routine delivery before 39 weeks is avoided.

Polyhydramnios is another listed complication — see amniotic fluid. Women with GDM also have a higher risk of hypertensive disorders — see pre-eclampsia and eclampsia.

• Growth scans: for every GDM pregnancy at 28–30 weeks and again at 34–36 weeks (at least 3 weeks apart), with biometry and amniotic fluid estimation; an anatomy scan if GDM is diagnosed before 20 weeks.
• Fetal surveillance: GDM raises the risk of fetal death in utero, especially in women needing drugs — fetal heart at every visit and daily fetal movement counting.
• Timing: routine delivery before 39 weeks is not recommended. If sugars are well controlled and labour has not started, induce at or after 39 weeks. Poor control, hypertension or a previous stillbirth justify earlier, individualised delivery.
• Mode: vaginal delivery is preferred; caesarean for obstetric indications. If the estimated fetal weight is above 4 kg, consider a primary caesarean at 39 weeks to avoid shoulder dystocia.
• On the day: the morning dose of insulin or metformin is withheld on the day of induction or labour, with glucose monitoring in labour.

Maternal glucose usually returns to normal after delivery, but the diagnosis is a warning: women with previous GDM have up to a sevenfold higher risk of type 2 diabetes (StatPearls). The Indian guideline asks for a 75 g OGTT (fasting and 2-hour) at 6 weeks postpartum; international guidelines suggest testing between 4 and 12 weeks after delivery.

Nonpregnant thresholds apply after delivery — see diabetes mellitus diagnosis and complications for the full criteria, and anti-diabetic drugs for metformin and insulin pharmacology.