GDM: Physical Activity (2008)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To examine the relationship between recreational physical activity before and during pregnancy and risk of gestational diabetes mellitus (GDM).
Inclusion Criteria:

Subjects were drawn from a larger study, designed to examine maternal dietary risk factors for preeclampsia.  The study population consists of women attending prenatal care clinics.  Women eligible for inclusion were those who initiated prenatal care prior to 16 weeks gestation. 

Exclusion Criteria:
Women were not eligible if they were younger than 18 years of age, did not speak and read English, did not plan to carry the pregnancy to term, and/or did not plan to deliver at either of the two research hospitals.  Women were also excluded if they were lost to follow-up, experienced a spontaneous or induced abortion, those for whom glucose tolerance test data were missing, those with preexisting diabetes mellitus and those for whom physical activity data were incomplete.
Description of Study Protocol:

Recruitment  At the initiation of the study researchers approached and enrolled nulliparous women who had completed >16 weeks of gestation.  Later, multiparous women were approached and enrolled when study personnel were available.

Design Prospective cohort study 

Blinding used (if applicable) Not mentioned

Intervention (if applicable)  Enrolled participants were asked to take part in a 45-60 minute interview in which trained research personnel used a structured questionnaire to elicit information regarding maternal sociodemographic characteristics, lifestyle habits, and medical and reproductive histories.  Participants were provided with a FFQ along with instructions for completing and returning.  Nonfasting blood and urine samples were collected in early pregnancy.  Pregnancy outcome information was ascertained by reviewing participants' hospital labor and delivery medical records or clinic records 7-9 months after participants were enrolled in the study.  Recreational physical activity during pregnancy was measured for the 7 days prior to the interview.

Statistical Analysis

The number of hours spent per week participating in recreational physical activity was calculated by dividing the total number of hours spent on each activity by the number of weeks during which the activity was performed and then summing these values over all reported activities.  Inactive women were specified as the referent group.  Physically active women were categorized below and above the median.  The medians were 4.2 hours for activities performed during the year before pregnancy and 6.0 hours during pregnancy.

Energy expenditure was calculated as described by Ainsworth et al., and was expressed in MET-hours per week.  Met hours per week were calculated by dividing the total number of hours spent on each activity by the number of weeks during which the activity was performed, multiplying the result by the activity intensity score and summing over all reported activities.

Risk of GDM was assessed in relation to weekly energy expenditure on recreational physical acitivty.

Frequency distributions of maternal sociodemographic characteristics and medical and reproductive histories according to maternal recreational physical activity before pregnancy were examined.

Generalized linear models were fit using a log-link function to derive relative risk and 95% confidence intervals.  To assess confounding, variables were entered into the generalized linear model one at a time and then the adjusted and unadjusted relative risks were compared. 

Final generalized linear models included covariates that altered unadjusted relative risks by at least 10% as well as those covariates of a priori interest (eg, advanced maternal age and prepregnancy adiposity).

The following covariates were considered confounders:  maternal age, race, parity, smoking during pregnancy, first-degree family hx of type 2; prepregnancy adiposity and annual household income.

When reporting adjusted relative risks, the authors refer to those adjusted for maternal age, race, parity and prepregnancy BMI. 

The authors also evaluated the model-fit statistics for models with and without cross-product terms.

 

Data Collection Summary:

Timing of Measurements:  At mean gestational age 12.7 weeks

Dependent Variables:

  • Risk of Gestational Diabetes (GDM)

Independent Variables:

  • Recreational physical activity during the year prior to pregnancy - Any physical activity, Time spent in activity (hours/week), Energy expended in activity (MET-h/week)
  • Recreational physical activity during pregnancy -- Any physical activity, Time spent in activity (hours/week), Energy expended in activity (MET-h/week)

Control Variables: Maternal age, prepregnancy BMI, parity, race

 

Description of Actual Data Sample:

Initial N: 1000 women

Attrition (final N): 909

Age: The below are based on prepregnancy activity levels.

Maternal Age

Not Active

Active < 4.2 hours/week

Active > 4.2 hours/week

  N             %        N                        % N                 %
<35 67 76.1 296 72.2 296 72
>35 21 23.9 114 27.8 115 28

Ethnicity:

 

Not Active

Active < 4.2 hours/week

Active > 4.2 hours/week

  N             %        N                        % N                 %

Non-White Race

22 25 66 16.1 52 12.7

Other relevant demographics:

 

Not Active

Active < 4.2 hours/week

Active > 4.2 hours/week

  N             %    N                        % N                 %
Unmarried 20              22.7         33 8.1 51 12.4
<12 years of education 11 12.6 22 5.6 8 2.0
Nulliparous 60 68.2 345 84.2 370 90.00
No prenatal vitamin use 5 5.7 11 2.7 9 2.2
Smoking during pregnancy 11 34.4 29 23.2 16 14.4

Annual Household Income

Not Active

Active < 4.2 hours/week

Active > 4.2 hours/week

  N             %        N                        % N                 %
<30,000 9 10.8 19 4.7 12 3.0
30,000-69,000 28 33.7 125 31.1 115 28.6
>70,000 46 55.4 258 64.2 275 68.4

Anthropometrics

Prepregnancy BMI

Not Active

Active <4.2 hours/week

Active >4.2 hours/week

  N             %        N                        % N                 %
<20 26 29.9 68 16.6 91 22.2
20-24.9 29 33.3 230 56.2 240 58.5
>25 32 36.8 111 27.1 79 19.3

Location: Two hospitals in Washington State, one in Seattle and one in Tacoma

 

Summary of Results:

Physical activity during the year before pregnancy

Any physical activity -- Compared with those who were inactive, women who participated in any recreational physical activity during the year before pregnancy experienced a 66% reduction in risk of gestational diabetes mellitus (RR = .34, 95%: .17, .70).  This association was attenuated somewhat after adjusting for maternal age, race, parity and pregpregnancy BMI (adjusted RR = .44;95%: .21, .91).

Time spent in activity (hours/week) -- Compared with inactive women, women who engaged in physical activity for <4.2 hours per week were 42 % less likely to develop gestational diabetes mellitus (adjusted RR = .58, 95%: .27, 1.24), although this association was not statistically significant.  Women who exercised >4.2 hours per week experienced a 76% reduction in risk (adjusted RR = .24, 95%: .10, .64). 

Energy expended in activity (MET-h/week) -- Likewise, energy expenditure was also associated with a reduced risk of GDM.  Expending <21.1 MET-hours per week (the median) on recreational physical activity was associated with a 43% reduction in risk (adjusted RR = .57, 95%: .27, 1.21) compared with inactivity, and expending >21.1 MET-hours per week was associated with a 74% reduction in risk of GDM (adjusted RR = .26, 95%; .10-.65).

Physical activity during pregnancy

Any physical activity -- During the index pregnancy, 615 women (67.7%) reported participating in any recreational physical activity.  Compared with inactive women, these women experienced a 31% reduction in risk for GDM (adjusted RR=.69, 95%: .37,1.29), although this association was not statistically significant. 

Time spent in activity (hours/week) -- The median number of hours per week spent performing recreational physical activities during this time period was 6.0.  Women who spent <6.0 hours per week engaged in physical activity were 58% less likely than women who were inactive to develop GDM (RR=.42, 95%: .19, .97).  This relationship was not significant after adjusting for maternal age, race, parity and prepregnancy BMI (RR=.49, 95%: .21, 1.13).  Participating in physical activity for >6.0 hours per week was associated with a 10% reduction in risk of GDM (adjusted RR = .90, 95%:.45, 1.8). 

Energy expended in activity (MET-h/week) -- Compared with inactive participants, those expending <28.0 MET-hours per week (the median) were 29% less likely to develop GDM (RR = .71, 95%: .35, 1.47) after adjusting for confounding factors.  Energy expenditure of >28.0 MET-hours per week was associated with a slightly reduced risk of GDM (adjusted RR =.67, 95%: .31,1.43), although statistical significance was not reached.

Other Findings

Of the 909 participants, 576 (63.4%), including 19 who developed GDM, were physically active both during the year before and during the index pregnancy.  Compared with inactive women, these participants  experienced a 73% reduction in risk of GDM (RR =.27, 95%: .11, .67).  The association was slightly attenuated after adjusting for maternal age, parity, race and prepregnancy BMI (RR = .31, 95%: .12, .79). 

Compared with inactivity, any physical activity during either of these time periods was associated with a reduced risk of GDM, although not statistically significant.

 

 

 

Author Conclusion:

Participation in any recreational physical activity during the year before pregnancy, compared with no physical activity, was related to a statistically significant reduced risk of GDM.

Time and energy expended performing physical activities during the time period before pregnancy were both associated with significant reductions in risk after adjustment for maternal age, race, parity and prepregnancy BMI.

While women engaging in physical activity during pregnancy were 31% less likely than inactive women to develop GDM, this association did not approach statistical significance.

Women who were physically active during both periods, however, experienced a 69% reduction in risk (RR = .31, 95%:.12, .79). 

Funding Source:
Reviewer Comments:

While reasons for the final N are described, they are not described separately for active vs. inactive women.

It is not clear at times throughout the manuscript which relationships were statistically significant.  The assumption appears to be that if significance is not mentioned then the relationship was significant.  Had the authors reported signficance levels in Tables 2 & 3, this would have been more clear.   Also, it would seem that if the adjusted RR was not significant then this should be the basis for conclusions, but this does not always appear to be the case.  For example, the authors conclude that "Time and energy expended performing physical activities during the time period before pregnancy were both associated with significant reductions in risk after adjustment for maternal age, race, parity and prepregnancy BMI", yet report, "Compared with inactive women, women who engaged in physical activity for <4.2 hours per week were 42 % less likely to develop gestational diabetes mellitus (adjusted RR = .58, 95%: .27, 1.24), although this association was not statistically significant."  It appears that the association was signficant only for those women who engaged in activity for 4.2 hours or more/week and suggest that women need a minimum number of hours of exercise to achieve a benefit.

It would have been nice to have seen prospective data related to stair climbing as presented in Dempsey JC, Butler CL, Diabetes Res and Practice, 2004.

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.) N/A
  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? Yes
  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? ???
  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? ???
  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? N/A
  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? ???
  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? N/A
  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? N/A
  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? 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? ???
  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? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? ???
  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)? Yes
  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