BMJ Study丨Why can't you stop gestational diabetes after desperately dieting before pregnancy?

Gestational diabetes mellitus (GDM), as the first hyperglycemic condition diagnosed during pregnancy, is affected by it in 1 in 7 live births worldwide, which not only increases the risk of type 2 diabetes and cardiovascular disease in the mother, but also may lead to obesity, diabetes and other problems in the offspring, forming an intergenerational cycle. To explore more effective prevention options, the BMJ published a randomized controlled trial showing that women at high risk of gestational diabetes did not significantly improve blood sugar control in the third trimester with time-restricted eating and exercise training from before pregnancy and throughout pregnancy.

Innovative intervention plan: pre-pregnancy start, two-pronged approach

The single-center randomised controlled trial, titled "BEFORE THE BEGINNING", included a total of 167 people at high risk of GDM and were randomly divided into intervention group (84 people) and control group (83 people). The core innovation of the study is to advance the intervention time to pre-pregnancy instead of the usual 16-20 weeks of pregnancy.

The intervention group adopts a combination of "time-restricted diet + exercise training": the diet requires all energy intake to be completed within ≤ 10 hours at least 5 days a week, and the eating window is no later than 7 pm; In terms of exercise, personal activity intelligence (PAI) is used as an indicator, and the goal is to accumulate ≥ 100 PAI points per week, mainly through high-intensity interval training (HIIT), participants wear smartwatches to record data, and the research team provides a home training instruction manual, supplemented by a small amount of supervised training. The control group received usual care and maintained their original diet and exercise habits.

Core results: No improvement in glycemic control and inhibition of weight gain

After long-term follow-up, the primary endpoint results of the study did not meet expectations. In the 75 g oral glucose tolerance test conducted at 28 weeks of gestation, there was no statistically significant difference in 2-hour plasma glucose concentrations in the intervention group compared to the control group (mean difference 0.48 mmol/L, 95% confidence interval -0.05 to 1.01, P=0.08). In addition, there was no significant improvement in key blood glucose-related indicators such as fasting blood glucose, glycated hemoglobin (HbA1c), and insulin resistance index (HOMA2-IR) before pregnancy and at various time points during pregnancy.

In terms of the incidence of GDM, there was no significant difference between the two groups: at 12 weeks of gestation, 5.9% (3/51) of participants in both groups met the diagnostic criteria for GDM; At 28 weeks of gestation, the incidence rate was 16.3% (8/49) in the intervention group and 11.5% (6/52) in the control group, and the difference was not statistically significant (P=0.57).

It is worth noting that the intervention group achieved significant results in weight management. At 28 weeks of gestation, the intervention group gained 2.0 kg less than the control group and lost 1.5 kg (95% CI -2.5 to -0.4, P=0.008), which was an important positive result of this study.

Challenge: Good pre-pregnancy performance and sustained decline during pregnancy

Adherence data on interventions revealed key issues in the implementation process. In the preconception phase, the average eating window in the intervention group was 9.9 hours, 49% of participants were able to stick to a time-restricted diet of ≤ 10 hours, and 43% reached the exercise goal of ≥100 PAI points per week. However, after entering pregnancy, compliance gradually declined: the proportion of adhering to time-restricted diets in the first, second and third trimesters dropped to 42%, 31% and 38% respectively, and the exercise compliance rate dropped to 29%, 18% and 15%, and the weekly PAI points also decreased significantly compared with before pregnancy.

There was no significant difference in self-reported energy intake and physical activity levels in the control group over the study period compared to the intervention group, which may have weakened the relative effect of the intervention. In addition, there was no significant difference in the time to conception between the two groups, with an average of 112 days in the intervention group and 84 days in the control group (P=0.10), but the fertile time was significantly extended (mean 48 days longer, P=0.005) in the intervention group who met the strict adherence criteria.

Research implications: Preconception intervention still has potential, and optimization is the key

Although it failed to improve core blood glucose indicators, this study still provides an important reference for GDM prevention. Studies have confirmed that the combined intervention plan of "time-restricted diet + HIIT" is feasible and can effectively control weight and fat mass growth during pregnancy, which is of positive significance for reducing the long-term metabolic risk of mother and baby.

The study also pointed out that factors such as decreased compliance during pregnancy and strong health awareness in the control group may be important reasons why the intervention did not meet expectations. In the future, intervention strategies need to be further optimized, such as strengthening pregnancy supervision, using more interactive digital health tools to improve adherence, and designing more precise programs for single high-risk factors (such as obesity alone, previous GDM history) to improve intervention effectiveness.

For clinicians, this study suggests that preconception intervention is an important window period for GDM prevention, but the strength of existing combination regimens may not be enough to improve glycemic control, and the intervention details need to be adjusted according to the patient's specific situation. For people at high risk of GDM, paying attention to dietary regularity and exercise habits before pregnancy is still an effective means to maintain health during pregnancy, especially in weight management.

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