GDM: Physical Activity (2008)

Citation:
 
Study Design:
Class:
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Quality Rating:
Research Purpose:
To evaluate the effect of a single session of exercise (cycling), at rest (control condition) and at two intensity levels (low and moderate intensity exercise conditions) on blood glucose and insulin levels in pregnancy complicated by gestation diabetes mellitus (GDM).  It was hypothesized that exercise at a moderate level of intensity (55% VO2 max) would lower blood glucose levels to a greater degree than exercise at a low level of intensity (35% VO2 max) as compared to the resting condition.
Inclusion Criteria:
  • Women had GDM at 30-34 weeks' gestation
  • Aged 18-38
  • Able to read and speak English or work with an interpreter
  • Not participating in a regular aerobic exercise program
  • Approval of the obstetric care provider (MD or CNM).
Exclusion Criteria:

Women were excluded for signs of:

  • Preterm labor
  • HTN
  • Multifetal gestation
  • Fasting hyperglycemia level of >140 mg/dl
  • Current participation in a regular exercise program
  • Lack of approval from the care provider.
Description of Study Protocol:

Recruitment  Women with GDM and no other medical or obstetric complications were recruited from a large health maintenance organization. 

Design:  Nonrandomized Crossover Trial 

Blinding used (if applicable) Not described

Intervention (if applicable)  Upon giving consent, each participant met with the investigators for baseline assessment.  This included collection of standard medical, obstetric and demographic data.  Ht, Wt and BMI were determined.  Participants then underwent a submaximal cycle ergometer graded exercise test to estimate VO2max.  The fetal heart rate was monitored for 15 min before and after the exercise test to assure fetal safety.   Heart rates and VO2 values from the submaximal graded exercise test were plotted and a 'line of best fit' was extrapolated to an estimated peak heart rate for each participant.  Heart rates and VO2 associated with 35% (low) and 55% (moderate) of their estimated VO2 peak were calculated and recorded as the predicted work rate intensity for each individual. 

Participants then visited the exercise laboratory on three occasions, once for the supervised 30 min rest session (sitting in a reclining chair) and twice for 30 min exercise sessions at 35% and 55% estimated VO2max.  Before attending these sessions, participants consumed a standard lunch consisting of two startch, two protein, one vegetable, one fruit and one milk exchange.  A record of food consumed was kept.

Statistical Analysis Blood glucose levels were analyzed using a doubly repeated measures ANOVA for each of the 11 blood drawing time periods across the three test conditions.  Bonferroni correction was used to control the overall alpha level because of significant time and test interaction.  The alpha level was set at .005 because of the repeated analyses.  The area under the curve was approximated for each test condition.  The area under the curve represents blood glucose concentration multiplied by time.  The three areas were compared by one-way ANOVA to evaluate differences in overall blood glucose changes among the three test condition.

With insulin levels, the slope of the time points of each test condition was calculated and the slopes for each test condition were compared using one-way ANOVA.

Repeated measures ANOVA was used to examine changes in hematocrit across each test condition.  Hemotocrit levels were used to convert whole blood values to plasma values.

Because the sample was heterogeneous for BMI, a secondary analysis was performed to examine the effect of exercise based on the pre-pregnant BMI.  Women were divided into two subgroups, group 1 had a BMI of <26 and group 2 had a BMI >26.  The relationship between insulin and BMI was calculated.

 

Data Collection Summary:

Timing of Measurements

For each session and the following two hours, blood glucose and insulin levels were drawn at 15 min intervals for a total of 11 samples.  Subsequent sessions took place between the 3rd and 7th day after the previous session.  Participants were called the morning after the session to collect their fasting blood glucose values.  Participants were instructed not to engage in any formal exercise.

Dependent Variables

  • Glucose Levels
  • Insulin Levels
  • Hematocrit

Independent Variables

  • Rest, or single session of exercise at 35% VO2max and 55% VO2max

Control Variables  Women served as their own controls

Description of Actual Data Sample:

Initial N: 14 women

Attrition (final N): 13, 12 for repeated measures ANOVA; 1 women dropped out due to lack of interest and one missed her 3rd session due to labor

Age: 18-38, mean 31.92 + 3.64

Ethnicity: Not specified

Other relevant demographics: Not specified

Anthropometrics

Variable Mean + SD Range
Weeks' gestation at dx of GDM 27.00 + 2.65 21-30
Height (in) 64.41 + 3.22 59-69
Pre-pregnant weight (lb) 186.00 + 33.66 142-254
Pre-pregnant BMI (kg/m2) 28.99 + 7.44 21-48
BMI during study (kg/m2) 31.84 + 6.12 25-47

Location: Exercise laboratory, University of Minnesota, Minneapolis.

 

Summary of Results:

Other Findings

There was no diffference in baseline in blood glucose levels.  The blood glucose level was significantly lower for each exercise condition compared to rest, and for moderate compared to low-intensity exercise (5.2 vs. 4.3 vs 3.9 mmol/l) at the end of exercise (30 min), and for the two exercise conditions compared to reast at 15 min after exercise (4.9 vs 4.4 vs. 4.0 mmol/l).  By 45 min after exercise, the blood glucose values were nearly identical. 

The area under the curve for blood glucose was signficantly lower for low- and moderate-intenstiy exercise than for rest (p=.01).  The slope of change in insulin amont the three conditions, from baseline to the 30 min session, approached signficance (p=.065).  The power for the analysis was .51. 

When the women were divided into subgroups based on BMI, there were seven in group 1 (Mean BMI 24kg/m2, SD 2.16) and six in group 2 (mean BMI 34 kg/m2, SD 6.99).  Correlation between the insulin slope and BMI for each test condition showed a significant negative correlation (-.643, p = .02) for the rest condition, but no significant correlation for low or moderate exercise.  No differences were found in insulin slope between the two groups.  One-way ANOVA was significant for group 2 (F =4.08, p =.039), rest vs moderate intensity exercise (p = .0012), but not for group 1.

 

Author Conclusion:

This study demonstrated an acute decline in blood glucose levels during low- and moderate-intensity exercise in women with GDM, compared to values at rest.  The decline was greater at higher intensity levels, as hypothesized, suggesting a dose-response effect, although the difference in blood glucose level between exercise intensities was only signficant at the end (30 min) of exercise.

Differences in area under the curve were not significant for low vs. moderate intensity, although the absolute difference was in the hypothesized direction.

When the women were grouped according to BMI, the area under the curve changed in the expected direction for each subgroup but was only statistically significant for the overweight women, suggesting a greater effect of exercise on blood glucose level in these women.

Funding Source:
Reviewer Comments:

The results show the importance of exercise, either low or moderate, following a meal in helping to decrease both blood glucose and insulin levels.

The authors address the issues related to power and indicate the need for larger sample sizes.  They do not indicate whether they were able to recruit the higher numbers needed, although, this may have strengthened their results had they done so.  The also allude to a need for a more culturally diverse sample, but did not describe the current sample with respect to ethnicity.

In agreement with the authors, it seems that the best method for controlling intake prior to exercise, would have been to serve a standardized meal and to ask participants to consume the meal in its entirety to ensure that the macronutrient content was universal for all, helping to control for macronutrient interactions.

 

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? ???
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? ???
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes