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].