DISCUSSION
This randomised clinical trial examined the effects of postmeal walking (PMW; 10-minute walks after three main meals) on measures of maternal glucose control and physical activity patterns compared to current standard-care physical activity recommendations in women with GDM. In contrast to our hypothesis, PMW was neither superior nor comparable to standard-care advice to walk/be physically active for ~30-minutes per day for both glycaemic and physical activity outcomes. Prior research had compared postmeal walking to a sitting control in acute settings [18], this is the first trial to compare a PMW intervention and include an active comparator; reiterating advice that is also standard care. Though both groups on average met the minimum physical activity recommendations, adherence to 10-min bouts after meals in the PMW group decreased to nearly half the recommended amount by 35 weeks and the PMW group spent more time in sedentary behaviours and less time in incidental activity across the intervention. This was unexpected as we had hypothesised that dividing 30-min into smaller bouts may be more achievable and by spreading them across the day this would reduce sitting time. The tendency for more sedentary behaviour and lower incidental activity for the PMW group was evident at baseline but also persisted throughout the intervention. This increase in sedentary behaviours likely counteracted the benefits of a 10-min walk and may explain the lack of results for many of the glucose outcomes.
Controlling maternal glucose concentrations are pivotal for the future health of both the women and children diagnosed with, or born to, a GDM pregnancy. Whilst our study found no differences in 24 h or nocturnal (fasting) glucose, there were effects on postprandial glucose. BMI-matched PMW group had a higher postprandial glucose over lunch and dinner compared to CTL, this was unexpected given PMW bouts were prescribed to reduce postprandial glucose after meals via contraction mediated uptake. These results may be due to 42% of the CTL group completing ~30-min walks at lunch (supplementary Figure 2); the exercise duration being three-fold longer than that recommended to PMW. Further, within the PMW there was a lower adherence to 10-min walks after dinner which may further explain the worsening postprandial mean and AUC across the afternoon/evening. In addition to the finding regarding adherence, the superior results with 30-min continuous suggests longer postmeal walks, or potentially higher intensity postmeal walks (intensity was recorded to be largely light intensity/pace of walking), are needed to influence postprandial glucose in women with GDM.
Given the well-known poor adherence to physical activity during pregnancy [20], strategies that make physical activity in pregnancy more palatable and achievable are urgently needed. Our study showed high adherence to achieving 30-min of daily walking, regardless of whether prescribed as accumulated bouts or one single bout. This may be due to selection bias of recruitment into an exercise-based study for women with GDM, both groups were considered physically active at baseline. We found that the small goal of 10 minutes of walking after main meals is achievable across the day, women exceeded the physical activity recommendations at 32 weeks and although this dropped off significantly at 35 weeks this was a similar trend in both groups. The high physical activity in both groups may also be a key factor in the normal birth outcomes reported for this sample. Future research would benefit from exploring utilising PMW to improve adherence to physical activity guidelines in less physically active women.
GDM is associated with an increased risk of many neonatal conditions such as hypoglycaemia, caused by hyperinsulinism, and macrosomia. It is reported that 53% of diet-controlled GDM neonates present incidences of hypoglycaemia [25], however, our study reported only one (4.5%) neonate with any hypoglycaemia excursions (n=1 CTL). Further, 15-45% of women with GDM deliver babies with macrosomia (> 4000 g birth weight) [26], yet only 3 (13.6%) neonates presented at this threshold in this study (n=2 CONT, n=1 PMW). Interestingly, increased standing time, and decreased sitting bouts > 30 minutes correlated to a larger neonatal birth weight. Our study agrees with previous literature (25, 26) that increased neonatal birth weight was correlated with an increased postprandial glucose. Whilst many studies [6, 25, 26] have explored the relationship between maternal glucose and neonatal outcomes, they did not control for diet or physical activity. The findings of this study suggest controlling maternal glycaemia and reaching physical activity guidelines are both beneficial in improving the birth outcomes of pregnancies with GDM, future research is needed into the effect of specific physical activity patterns.
This is the first study to explore postmeal walking in free-living women with GDM from their initial diagnosis to delivery. In contrast to previous research, interventions were time matched to the current standard care physical activity guidelines (3 x 10 minutes vs 30 minutes continuous)[10, 18]. The proposed intervention of PMW is scalable and simple to deliver, however our findings indicate further research on mitigating sedentary behaviour and increasing steps per day in pregnancy, in addition to prescribing physical activity, is warranted. A major strength of this study is the use of a continuous measurement period of glucose responses, after meals and overnight, in response to interventions. This is important given the emphasis on tight glycaemic ranges for GDM management of fasting and postprandial. Similarly, another strength of this study is the use of an inclinometer for objective physical activity and adherence measurement. This is important given its ability to provide an objective measure of physical activity and provide exact times exercise began and finished, exercise intensity and duration of bouts; all of which can inform future research. There are also several limitations to acknowledge. We finished up with a smaller sample size with a higher than anticipated number of dropouts in the study, largely experienced due to the COVID-19 pandemic. Previous research recommended at least 12 participants per group for pilot studies may be valid in providing sufficient data to further inform larger trials [27].