GDM: Macronutrients (2008)

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

To characterize and determine the predictors of birth weight among women with gestational diabetes mellitus and to establish whether these predictors vary by prepregnancy BMI.

Inclusion Criteria:
  • Diagnostic criteria of National Diabetes Data Group for gestational diabetes:  >2 OGTT values (fasting 5.8, 1-hr 10.6, 2-hr 9.2, 3-hr 8.1 mmol/L)
  • Class A1: controlled by diet and Class A2: controlled with diet + insulin
Exclusion Criteria:
  • Incomplete data
  • Pregestational diabetes
  • Impaired glucose tolerance
  • Premature delivery
  • Medical conditions of mothers or infants
Description of Study Protocol:

Recruitment: 

Retrospective chart review of 1003 patients at the Royal Victoria Hospital Antenatal Diabetic Clinic, Montreal, Canada 1978-1989.

Design:  Cohort Study

Blinding Used (if applicable):  not applicable

Intervention (if applicable):

  • Monitoring q wk by multidisciplinary team + daily self monitoring
  • Counseling by RD on diet 35 kcal/kg or adjusted for glycemic and weight control
  • Weekly evaluations of fasting and 1-hr postprandial serum glucose, dietary adherence, weight changes, blood pressure, ultrasonography (q 3-4 wk) and nonstress test for fetal well being
  • Self-monitoring: daily food records, urinalysis for glucose and ketones, glucose monitoring 4 times/d if needed, insulin therapy if fasting blood glucose >5.0 mmol/L, h-hr, >6.7 mmol/L

Statistical Analysis

Analyses by BMI groups were done with ANOVA and chi-square tests, intergroup differences were measured with Scheffe and chi-sqaure tests.  Predictors of birth weight were examined by using multiple linear regression and predictors of macrosomia by multiple logistic regression.

Data Collection Summary:

Timing of Measurements:

Monitoring q wk by multidisciplinary team + daily self monitoring.

Dependent Variables:

  • Birth weight

Independent Variables

  • Counseling by RD on diet 35 kcal/kg or adjusted for glycemic and weight control
  • Weekly evaluations of fasting and 1-hr postprandial serum glucose, dietary adherence, weight changes, blood pressure, ultrasonography (q 3-4 wk) and nonstress test for fetal well being
  • Self-monitoring: daily food records, urinalysis for glucose and ketones, glucose monitoring 4 times/d if needed, insulin therapy if fasting blood glucose >5.0 mmol/L, h-hr, >6.7 mmol/L

Control Variables

Description of Actual Data Sample:

Initial N:  353 women met criteria for being in the study and all delivered live full-term infants (>37 wk).

Attrition (final N):  353 women

Age:  mean 31.6 +/- 5.1 years

Ethnicity:  70.7% White

Other relevant demographics:

Anthropometrics:

Location:  Canada

Summary of Results:

Mean kcal intakes that met goals of weight gain and metabolic control (blood glucose, urine ketones) were as follows:

Prepregnancy weight Kcal/kg
Underweight 43

Normal weight

35

Overweight

30
Obese 24

Data presented by prepregnancy body weight.  Dietary intake was similar for all groups (underweight, normal, overweight, obese).

  Ranges 
Kcal: 2046 - 2072
Carbohydrate, g 117-  177
(%)    23 – 34

Fat, g  

106-108
(%)  43-47

Protein, g  

99-102

Other Findings

Dietary treatment decreased the rate of weight gain from 0.35 to 0.16 kg/wk, P<0.0001, and fasting serum glucose from 4.8 to 4.2 mmol/L, (P<0.001).

Positive predictors of infant birth weight among the underweight and normal weight women (BMI <26) were prepregnancy BMI, height, parity, prediagnostic rate of weight gain, postpriandial serum glucose and gestational duration.

Among the overweight women (BMI >26) the only variables that predicted increased­ birth weight were prediagnostic rate of weight gain, fasting or postprandial serum glucose.

Author Conclusion:

Prepregnancy BMI exerts a strong effect on predictors of infant birth weight in women with gestational diabetes, suggesting a need to consider prepregnancy weight in the treatment approach.

Moderate dietary restriction alone can decrease both the rate of weight gain and fasting serum glucose among women with gestational diabetes, emphasizing the important role of diet in the management of gestational diabetes. 

Women with prepregnancy BMI  >26 should be identified and treated early to limit excessive weight gain, attain euglycemia and thereby decrease the risk of macrosomia.

Funding Source:
Government: NSERC
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:

Very low carbohydrate intakes (~<40%) and high fat intakes (~45%). Not clear if dietary intakes were considered in the regression model.

Well designed and controlled study with RD intervention and adjustment of diet or addition of insulin for appropriate weight gain and glycemic control.

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? 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? 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? N/A
  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? 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.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  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? Yes
  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? N/A
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)? 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