Gestational diabetes mellitus (GDM) is a form of diabetes that develops during pregnancy in women who did not have diabetes before. It affects approximately 2–10% of pregnancies worldwide and, if well managed, usually resolves after delivery. However, it requires careful monitoring because it can affect both the mother and the baby if left untreated.
During pregnancy, the placenta produces hormones that help the baby grow but also make the mother's cells more resistant to insulin. Normally, the pancreas compensates by producing more insulin. In women who develop gestational diabetes, the pancreas cannot keep up, and blood glucose levels rise too high.
Risk factors include being overweight or obese before pregnancy, a family history of type 2 diabetes, having had gestational diabetes in a previous pregnancy, being over 25 years of age, having polycystic ovary syndrome (PCOS), and being from certain ethnic backgrounds (South Asian, Black, Middle Eastern, and Hispanic women are at higher risk).
Gestational diabetes often causes no noticeable symptoms, which is why routine screening is recommended for all pregnant women. When symptoms do occur, they can include increased thirst, more frequent urination than usual for pregnancy, fatigue, and blurred vision — all of which overlap with normal pregnancy experiences. This is why the glucose tolerance test is the only reliable way to diagnose the condition.
Most healthcare providers screen for gestational diabetes between weeks 24 and 28 with a glucose challenge test. You drink a sugary solution containing 50 grams of glucose, and your blood is drawn one hour later. If the result is above the threshold, you will be asked to take a longer oral glucose tolerance test (OGTT), which measures blood glucose fasting and at intervals after consuming a larger glucose dose.
For the baby: High blood sugar crosses the placenta, causing the baby to produce excess insulin. This can lead to macrosomia (a very large baby, increasing the risk of delivery complications), low blood sugar in the newborn after birth, premature birth, and a higher lifetime risk of obesity and type 2 diabetes.
For the mother: Gestational diabetes increases the risk of preeclampsia, the need for caesarean delivery due to a large baby, and developing type 2 diabetes later in life (up to 50% of women with GDM develop type 2 diabetes within 10 years).
Diet and meal planning is the cornerstone of GDM management. A registered dietitian can help you create a meal plan that controls carbohydrate intake, spreads carbohydrates evenly across meals and snacks, and emphasises low-glycaemic-index foods such as wholegrains, legumes, and non-starchy vegetables. Sugary drinks, refined carbohydrates, and processed foods should be minimised.
Regular physical activity improves insulin sensitivity and helps control blood sugar levels. Walking after meals is particularly effective — a 15-minute walk after eating can noticeably reduce the post-meal glucose spike.
Blood glucose monitoring involves testing blood sugar several times a day, typically fasting and one to two hours after meals, using a home glucose meter. Your healthcare team will give you target ranges to aim for.
Medication — insulin injections or oral medication such as metformin — may be required if diet and exercise alone do not achieve target blood glucose levels. Both are safe in pregnancy when used as directed.
Blood glucose levels usually return to normal shortly after birth. However, gestational diabetes increases your long-term risk of type 2 diabetes, so a glucose test is recommended 6–12 weeks postpartum and annually thereafter. Maintaining a healthy weight, eating well, and staying physically active significantly reduce this long-term risk.
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This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider regarding your specific situation.