A systematic review on the role of diet in managing pre-existing diabetes during pregnancy.

Pre-existing diabetes in pregnancy is rising globally and is associated with significant maternal and neonatal health risks, yet optimal dietary strategies remain uncertain. This systematic review evaluated evidence on dietary components, supplements and dietary patterns during pre-conception and pregnancy in women with pre-existing diabetes. Electronic databases were searched for eligible studies, and risk of bias was assessed using ROB-2, ROBINS-E and ROBINS-I-V2. A random-effects meta-analysis with GRADE assessment was conducted for folic acid supplementation. Twenty-six studies from ten countries met inclusion criteria. Higher diet quality characterised by greater intakes of vegetables, fruits, plant-based proteins, nuts, fish, and lower intakes of processed foods was associated with improved glycaemic outcomes. Low-glycaemic index and DASH dietary patterns, along with carbohydrate counting showed potential benefits, while evidence for low carbohydrate and high-fibre diets was mixed. Associations with gestational weight gain, pre-eclampsia, and neonatal outcomes were inconsistent. Meta-analysis suggested pre-conception folic acid supplementation reduced neural tube defect risk, however the certainty of evidence was very low. Diet quality appears more important than specific macronutrient targets and individualised dietitian led care is essential. Further high-quality research is needed to define optimal dietary approaches for pregnancies complicated by pre-existing diabetes.