Dietary approaches to managing diabetes in pregnancy
Approximately one in six pregnancies worldwide are affected by diabetes, including both pre-existing diabetes and gestational diabetes mellitus (GDM), which is first recognised during pregnancy and resolves after delivery. Suboptimal management of hyperglycaemia increases the risk of pre-eclampsia, preterm birth, excessive fetal growth, birth injuries, neonatal hypoglycaemia, and long-term future risk of type 2 diabetes. Diet and lifestyle modifications are the cornerstone of diabetes management, particularly for GDM, yet current recommendations lack specificity and a robust evidence-base. The overall aim of this thesis was to examine the interplay between maternal diet, glycaemia and weight gain in women with diabetes in pregnancy. This thesis comprises four distinct projects. Firstly, a systematic review and meta-analysis were conducted to examine the relationship between dietary fibre and glycaemic control in women with diabetes in pregnancy. Subgroup analysis and meta-regression explored sources of heterogeneity. Second, a prospective observational study investigated dietary and physical activity patterns of women with one or more risk factor for GDM. Data were collected using a 24-hour diet recall (Intake24) and Recent Physical Activity Questionnaire (RPAQ), and associations were assessed with maternal characteristics and glucose outcomes from an oral glucose tolerance test (OGTT). Third, the Dietary Intervention in Gestational Diabetes (DiGest) trial; a randomised, double-blind, whole-diet intervention study evaluated the effect of a reduced-energy diet (1200kcal vs 2000kcal) on maternal weight change and infant birthweight in women with GDM, alongside other key maternal and neonatal outcomes. Finally, a cross-sectional secondary analysis of this trial cohort explored associations between baseline dietary and physical activity patterns and glycaemic control, measured by continuous glucose monitoring (CGM). The analysis also assessed trial adherence and examined the interaction between baseline dietary and physical activity patterns and the effectiveness of the intervention on maternal weight change. High fibre diets improved fasting glucose (Mean difference (MD) -0.35 mmol/L, 95 CI% -0.53, -0.18; p<0.01), postprandial glucose (MD -0.90 mmol/L, 95 CI% -1.39, -0.40; p<0.01), and reduced the likelihood of requiring insulin therapy for women with GDM (Odds ratio (OR); 0.24, 95% CI 0.13, 0.46;p<0.01), though no change in glycated haemoglobin (HbA1c) was observed (p>0.05). Among women at risk of developing GDM, smoking and multiparity were identified as determinants of a lower adherence to a prudent diet, while achieving >150 minutes of moderate physical activity per week was associated with a higher adherence. Dietary patterns alone were not strong predictors of glycaemic measures in this population. Paradoxically, a higher adherence to a prudent diet was associated with a higher 2-hour postload OGTT glucose value. This could be a spurious finding due to reverse causality and requires further examination with improved dietary assessment methods. In the DiGest trial, a reduced-energy diet in late pregnancy lowered the likelihood of requiring long-acting insulin (OR; 0.36, 95% CI 0.18, 0.70; p=0.003), however no difference in maternal weight change or infant birthweight was seen between trials arms. As the control group were assigned a calorie intake (2000 kcal) substantially lower than recommended (~2800 kcal) and had a calorie deficit larger than anticipated due to higher BMI at enrolment, both groups showed low weight gain during the intervention, below international guidelines. Higher baseline diet quality was associated with higher study adherence and an apparent intervention effect on weight loss. Exploratory analyses indicated that weight loss of 3kg, irrespective of intervention assignment, was associated with improved maternal and infant weight, as well as antenatal and postnatal glycaemia. No association was found between energy, carbohydrates, protein, fat or fibre and any measure of glycaemia. Most women were not adhering to the current dietary and physical activity guidelines for pregnancy or GDM management. To conclude, these findings reinforce the importance of dietary quality and physical activity in the management of diabetes in pregnancy. While high-fibre and reduced-energy diets showed potential for improving glycaemic control and reducing insulin use, the suboptimal quality of current dietary patterns suggest that clearer, evidence-based guidelines are urgently needed. Tailored interventions that support sustainable behaviour change may enhance outcomes for both mother and baby.
diabetes in pregnancy, dietary intervention, maternal glycaemia, continuous glucose monitoring
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