GDM: Physical Activity (2008)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To examine the effectiveness of a partially home-based, moderate-intensity aerobic exercise program for women with gestational diabetes with the expectation that such an exercise program would result in decreased blood glucose levels.

Inclusion Criteria:

1.       Physician or certified nurse-midwife diagnosis of GDM

2.        <34 wk gestation

3.        no other important medical or obstetric complications

4.        ability to read and write English

5.        18-40 years of age

6.        no current regular exercise regimen for continuous 30-minute periods more than twice/week

 

Exclusion Criteria:
Not described.
Description of Study Protocol:

Recruitment:  Women from a large midwestern health maintenance organization were potential subjects.  Associated clinics were telephoned weekly to inquire about possible subjects.  All women diagnosed with GDM and referred by the care provider who met the study criteria were invited to participate.

Design:  randomized trial

Blinding used (if applicable):  Subjects not blinded to the study intervention

Intervention (if applicable): 

Subjects were randomly assigned to an exercise or no exercise group.

Statistical Analysis: Univariate tests were used to compare groups with a signficance of p < .05.  Continuous or interval data were analyzed using the student t test.  Paired and unpaired t tests were performed to examine between and within grop differences.  For those subjects who were in the study for 8 weeks and had 3 HgbA1Cs performed a repeated-measures ANOVA was used.  Variables with nominal or ordinal data were analyzed using nonparametric methods.

Data Collection Summary:

Timing of Measurements:  Women enrolled in the study at 34 weeks EGA or less.  Subjects had already been educated in home blood glucose monitoring and had had dietary counseling before entering the study.  Cardiorespiratory fitness was measured at baseline and at term using a submaximal cycle ergometer test and the Astrand-Rhyming nomogram with age corrections, which predicts maximal oxygen consumption from the heart rate at a known submaximal work load.  Subjects were familiarized with the protocol through a practice test prior to the first actual test. Maternal heart rate was monitored throughout the test.  Fetal heart rate was monitored before and after the exercise test as were uterine contractions.

Dependent Variables: 

  • Experimental subjects exercised for 30 minutes, 3-4 times/wk at 70% maximal heart rate for the remainder of the pregnancy.  This included a 5 minute warm-up and 5 minute cool down.
  • 2 times/wk the exercise was performed on a cycle ergometer in the presence of the investigator and maternal heart was monitored continuously.
  • 1 time/wk, fetal monitoring was performed before and after exercise.
  • 1 to 2 times/wk, the subjects exercised on their own and recorded the time and amount of exercise.  Subjects were taught to check and record their heart rate at 10 and 20 minutes and were asked to rate their perceived exertion twice when they checked their heart rate.  Subjects were assigned a rating of perceived exertion level that corresonded to their training heart rate to keep the exercise intensity as similar as possible for supervised and unsupervised sessions.  Subjects could walk or cycle for the unsupervised sessions and most women chose to walk.
  • Control subjects continued dietary therapy and usual physical activity levels.  They were telephoned weekly by the investigator to monitor progress and were instructed to record the date, type and amount of exercsie they performed.
  • Three days per week, all subjects made fasting and 2h postprandial blood glucose determinations and logged.  Measurements of HgbA1C were made at baseline and at 4 week intervals.
  • Insulin tx, if required, was noted during data collection.
  • Dietary intake measured using a Willett Semi-Quantitative FFQ at baseline and at term
  • Newborn hypoglycemia

Independent Variables: 

  • Physical activity measured using the Baecke Questionnaire

Control Variables: No control variables.  A control group was used.

Description of Actual Data Sample:

Initial N:  33

Attrition (Final N): 29:  exercise group - 15 and control group - 14; 1 in the experimental group dropped out and 3 subjects in the control group were withdrawn for medical reasons

Age: 18-40 years old

Ethinicity:  Predominantly Caucasian, 2 were Japanese

Other Relevant Demographics: Women in the two groups were similar for weeks' gestation at dx of GDM, 3h GTT results, cigarette smoking incidence, baseline HgA1C, and cardiorespiratory fitness.  Habitual activity was similar between the groups for sport, leisure and work indices. Baseline dietary data were similar for the two groups. 

Anthropometrics:  Height, pre-pregnancy weight, weight at baseline and term and BMI were not significantly different for the two groups.   Both groups were of similar height (mean height 63.4 + 2.5 inches for exercise group and 63.7 + 2.1 for controls) and overweight (mean BMI 28.4 + 7.6 for experimental group, 25.5 + 5.5 for controls) at study entry.

Location:  Nurse Midwifery Program, University of Minnesota.

Summary of Results:

Fasting and postprandial blood glucose levels (see table below), HgA1C, incidence of exogenous insulin therapy, birthweight, Apgar scores at 1 and 5 minutes and incidence of newborn hypoglycemia were not different between the groups.

Maternal Outcomes for the Experimental and Control Groups: Home Blood Glucose Levels

Variable

Experimental

Control

P

Fasting 78 + 9.8 (10) 77 + 7.6 (12) .8
2 h post breakfast 86 + 12.7 (10) 96 + 16.3 (12) .1
2 h post lunch 91 + 12.5 (10) 95 + 13 (12) .4
2 h post dinner 96 + 12.9 (10) 104 + 12.3 (12) .1

The experimental group exercised an average of 3.0 + .6 per times per week and controls exercised a mean of .7 + .6 times per week (P <.001).  The exercise group increased their cardiorespiratory fitenss by 10% and the control goup by 5%.  The change was significant for the exercise group (P =.005), but not the controls.

There were no differences in either group from baseline to post-study for total kcal or daily grams of protein, fat, or fiber.  There was, however, a significant decline in daily grams of carbohydrate consumed in the control group (P = 0.03) but not in the exercise group.

There were significant increases in sport, leisure, and total activity for the experimental group (P = .01, .03, and .002, respectively), but not for controls.

Average weekly maternal weight change was not different between the groups. 

Author Conclusion:

The authors speculate that there were no differences on the main variables of interest perhaps in part because the level of exercise intensity was not high enough.  Several members of the exercise group reported that their perceived exertion was lower during home based exercise sessions.  In addition, the sample size may have made it impossible to detect differences between groups.  Power calculations reported by the authors in the discussion demonstrated this.

A partially home-based exercise program did not reduce blood glucose levels, but did result in a modest increase in cardiorespiratory fitness. The intervention appeared safe.  Safety is supported in this study by the similarity in Apgar scores, gestational age at birth, and cesarean rate between study groups, and the lack of complications.

Funding Source:
Government: NIH
Industry:
Boehringer Manheim Corp.
Pharmaceutical/Dietary Supplement Company:
Not-for-profit
1
Foundation associated with industry:
Reviewer Comments:

Well designed and controlled study.

It is not clear if the power calculations were performed before or after study completion as they are reported in the discussion.  The authors mention that perceived lack of time prevented many eligible women from participating in the study.  Also, limitations with respect to funding, population, timeframe, etc, are not known, but it would be interesting to see the results of such a thorough study in a larger population. 

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? Yes
  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? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
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) Yes
  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? No
  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? ???
  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.) ???
  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? N/A
  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? Yes
  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)? N/A
  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? N/A
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