EAL

GDM: Physical Activity (2008)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

This study was designed to compare the extent and the rate to which blood glucose levels decrease in pregnant (25-35 weeks gestation) and nonpregnant women in response to 1 hour prolonged moderate intensity exercise (55% VO₂max), and also determine and compare the levels of circulating hormones and substrates that contribute to glucose homeostasis in pregnant and non pregnant women in response to exercise.

Inclusion Criteria:

Pregnant women (25 - 35 weeks gestation) - randomly selected

Non pregnant women - matched to pregnant women according to fitness level, confirmed by VO₂ max

All women were within their reproductive years, and nonpregnant women had normal menstrual cycles
Subjects signed informed consents and obtained medical clearance from their physicians before participating in the study

Exclusion Criteria:

abnormal EKG readings
abnormal blood pressure
abnormal fetal heart rate
medical or obstetrical complications

Description of Study Protocol:

Recruitment: Not described

Design: Non-randomized trial with concurrent controls

Blinding Used (if applicable): Not described

Intervention (if applicable) - Study Protocol:

1. Maximal oxygen consumption test (Vo₂max)

2. 60 minute continuous submaximal test at 50% to 60% of Vo₂max at a rate of 60 rpm.

During this time 7 samples containing 6 mL of blood were drawn using a sterile 3 way stopcock; blood was collected after 30 minutes of bedrest, just before the initiation of exercise, during exercise at 15, 30, 45 & 60 minutes, and at 30 minutes post exercise. The subjects were at least 2 hours post-absorptive before beginning this test.

Both tests were performed on Collins' Pedal Mode ergometers.

3. Other data collected during the 60 minutes of exercise at 15, 30, 45 & 60 minutes were (1) rating of perceived exertion using the Borg Scale (2) core temperature (3) maternal heart rate (4) and blood glucose as measured by Glucostix reagent strips.

4. At the completion of the 1 hour test, women were placed in a semi-recumbent position and rested while fetal heart rate was again monitored for a period of 15 minutes.

5. At the end of this 15 minute period, the last blood sample and core temperature reading were collected.

Statistical Analysis: Not clearly described. Means and signficance levels reported and between group analysis mentioned along with significance levels.

Data Collection Summary:

Timing of Measurements During study protocol 7 samples containing 6 mL of blood were drawn using a sterile 3 way stopcock; blood was collected after 30 minutes of bedrest, just before the initiation of exercise, during exercise at 15, 30, 45 & 60 minutes, and at 30 minutes post exercise. The subjects were at least 2 hours post-absorptive before beginning this test.

Dependent Variables

VO₂max - maximal oxygen consumption, repiratory exchange ratio(RER) during maximal and submaximal exercise, submaximal oxygen consumption and percentage of VO₂max, maximal and submaximal heart rate, percentage of maximal heart rate.
Submaximal test - Blood glucose, lactate, insulin, b-hydroxybutyrate, free fatty acids, temperature and perceived exertion

Independent Variables:

Activity, moderate prolonged exercise

Control Variables: No variables. Nonpregnant controls used.

Description of Actual Data Sample:

Initial N: 20, 10 pregnant and 10 nonpregnant

Attrition (Final N): 20

Age: see table below

Ethnicity: Not described

Other relevant demographics: Not described

Anthropometry: see table below

Location: Department of Exercise Sciences & Obstetrics and Gynecology, USC, Los Angeles, CA

Pregnant Non Pregnant

N 10 10

Age 33.3 + 1.6 29.4 + 1.4

Height (in) 5.5 +.07 5.4 + .06

Weight (lbs) 150.8 + 3.4 145.4 + 8.6

Gestation (wks) 27.1 + 1.3

Activity Level 2.6 + .3 2.4 + .2

Age, height, weight and activity level were not significantly different. For all pregnant women but one, the current pregnancy represented their first pregnancy. 3 out of the 10 non pregnant women had children. All women were within their reproductive age and were premenopausal.

Summary of Results:

Other Findings

1. VO₂max -- Both RER during maximal exercise and percentage of maximal heart rate were significantly different for pregnant and non pregnant participants.

2. Submaximal Test:

Glucose - The blood glucose levels of pregnant women decrease at a faster rate and throughout exercise, whereas non pregnant participants showed a drop in blood glucose at 15 minutes, but levels remained fairly constant from this point on. Between group analysis showed significant differences (p<.05) in blood glucose levels at 30, 60 and 15 minutes post exercise with pregnant women exhibiting lower values.

Lactate - Both groups showed an increase at 15 minutes with a subsequent drop with continued exercise and rest. Pregnant women showed lower levels of lactate at 60 minutes (p<.05) - this was the only significant difference between groups.

Insulin - Insulin levels of pregnant and nonpregnant women decreased to a significantly lower level between rest and 15 minutes of exercise, with the pregnant group showing a more dramatic drop. Pregnant women showed significantly higher levels at the beginning of exercise and significantly lower levels at the end of recovery (p<.05).

B-hydroxybutyrate increased significantly in both groups after 60 minutes of exercise (P<0.001). The patterns of increase were slightly different, however, there were no significant differences between groups.

FFA - results unable to be provided due to sampling problems.

Temperature - Increased for both groups and was significantly greater (p<.0001) at 60 minutes. No differences were noted between groups.

Perceived Exertion -- No within or between subjects differences were found.

VO2max - Reduced RER and %VO2max heart rate suggest that there might be an upper limit of intensity at which cardiac acceleration is blunted, possibly as a protective mechanism for the proper functioning of the maternal-fetal environment. Also as protection against the development of hypoglycemia.

Submaximal:

Intensity and duration play a significant role for both pregnant and nonpregnant women in the ability to maintain glucose levels.

Author Conclusion:

Pregnant women, unlike non pregnant controls, do not seem to reach a steady state with respect to glucose levels exhibiting faster and more pronounced decreases. This suggests differences in the rate and kinetics of blood glucose between pregnant and nonpregnant women.

The results also indicate significant differences in the level of circulating substrates and hormones between pregnant and nonpregnant women in response to exercise.

Insulin provided similar stimuli to both groups of women despite the higher needs of pregant women for alternative susbtrates.

The maternal glucose at 60 minutes of prolonged exercise (65.88+3.06 mg/dL) was comparable with that reached after 24 hours of maternal fasting (63.2 + 2.3mg/dL). This evidence suggests that with the low levels of glucose, the needs of the fetus may be compromised for the needs of the mother during exercise. Whether fetal hypoglycemia indeed occurs during exercise and what the long-term impact on the fetus would be, are issues that need to be further researched.

Funding Source:

Reviewer Comments:

This research suggests that snacks before and after exercise are important in women during pregnancy to prevent hypoglycemia and elevated ketones.

There is no information related to race.

Statistical analysis are not clearly described.

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)	???
	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)	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?		???
	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%.)	???
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	???
	4.4.	Were reasons for withdrawals similar across groups?	???
	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?	???
	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?	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?	Yes
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?	N/A
	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?		???
	8.1.	Were statistical analyses adequately described and the results reported appropriately?	No
	8.2.	Were correct statistical tests used and assumptions of test not violated?	???
	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)?	Yes
	8.6.	Was clinical significance as well as statistical significance reported?	???
	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?		???
	9.1.	Is there a discussion of findings?	Yes
	9.2.	Are biases and study limitations identified and discussed?	???
10.	Is bias due to study's funding or sponsorship unlikely?		???
	10.1.	Were sources of funding and investigators' affiliations described?	No
	10.2.	Was the study free from apparent conflict of interest?	???