Gestational diabetes mellitus is a form of diabetes that develops during pregnancy, characterised by impaired glucose tolerance sufficient to meet diagnostic criteria but not present before pregnancy. It affects approximately 5 percent of pregnancies in the UK, a figure that has risen substantially alongside increasing rates of pre-pregnancy overweight and obesity. Gestational diabetes carries risks for the mother, including an elevated risk of progression to type 2 diabetes within 10 years of the affected pregnancy, and for the baby, including macrosomia, birth complications, hypoglycaemia, and an increased long-term risk of obesity and metabolic syndrome.
The Physiology: Why Pregnancy Creates Insulin Resistance
In the second and third trimester, placental hormones including human placental lactogen, oestrogen, and progesterone progressively increase maternal insulin resistance. This is physiologically appropriate: it redirects maternal glucose toward the fetus by reducing maternal glucose uptake. In women with sufficient pancreatic beta-cell capacity, insulin secretion increases to compensate and blood glucose remains normal. In women with underlying insulin resistance, reduced beta-cell reserve, or other metabolic vulnerabilities, this compensatory capacity is exceeded and gestational diabetes develops. Women with gestational diabetes have, in essence, a stress-test of their metabolic reserve that reveals pre-existing vulnerability.
Risk Factors and Screening
NICE identifies the following as risk factors warranting gestational diabetes screening with an oral glucose tolerance test at 24 to 28 weeks: BMI above 30, a previous baby weighing 4.5 kilograms or more, a previous diagnosis of gestational diabetes, a first-degree relative with type 2 diabetes, and family origin from South Asian, Black Caribbean, or Middle Eastern backgrounds, which carry higher baseline insulin resistance risk. Women with any of these risk factors should ensure they are screened and should begin blood sugar management strategies from early pregnancy.
Dietary Strategies That Reduce Risk and Aid Management
A dietary pattern that supports blood glucose stability throughout pregnancy reduces both the risk of gestational diabetes and its severity if it develops. The most evidence-based approach involves a low-glycaemic index dietary pattern: replacing refined carbohydrates with wholegrains, legumes, and vegetables, eating protein and fat before carbohydrate at each meal, distributing carbohydrate evenly across three to four meals rather than concentrating it in one or two, and avoiding sugar-sweetened beverages. A randomised controlled trial by Markovic et al. found that a low-GI diet started early in pregnancy significantly reduced gestational diabetes incidence compared to healthy eating guidelines in women at risk. Regular moderate exercise, which reduces post-meal blood glucose through muscle glucose uptake, is equally important.
- Replace refined carbohydrates with wholegrain alternatives throughout pregnancy: oats, sweet potato, lentils, and quinoa over white bread, white rice, and processed cereals
- Start meals with vegetables and protein before eating carbohydrate: food order has a significant effect on postprandial blood glucose
- Walk for 10 to 15 minutes after each main meal: post-meal walking reduces blood glucose peaks by increasing muscle glucose uptake
- Avoid sugar-sweetened drinks entirely during pregnancy: they deliver glucose rapidly without satiety signals
- If you have any risk factors, discuss early glucose monitoring with your midwife rather than waiting for the standard 24-week screen
Sources
- NICE. (2015, updated 2023). Diabetes in pregnancy: management from preconception to the postnatal period (NG3). National Institute for Health and Care Excellence.
- Markovic, T.P., et al. (2016). Randomized controlled trial of a low glycemic index diet in gestational diabetes. Diabetes Care, 39(1), 31-38.
- Bø, K., et al. (2016). Exercise and pregnancy. British Journal of Sports Medicine, 50(10), 571-589.