GDM: Macronutrients (2008)

Citation:

Major CA, Henry MJ, De Veciana M, Morgan MA.  The effects of carbohydrate restriction in patients with diet-controlled gestational diabetes.  Obstet & Gynecol 1998;91:600-604. 

Worksheet created prior to Spring 2004 using earlier ADA research analysis template.
PubMed ID: 9540949
 
Study Design:
Non-Randomized Controlled Trial
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To determine the effect of carbohydrate restriction on perinatal outcome in patients with diet-controlled gestational diabetes mellitus.

Inclusion Criteria:
  • Diagnosis of GDM by 100-g, 3-hr OGTT with > 2 abnormal glucose values.
  • Fasting blood glucose were not  >105 mg/dl
Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment

All women received prenatal care at UC, Irvine between June 1993 and June 1994.

Design:  Nonrandomized Trial with Concurrent controls. Half of the women were nonrandomly assigned to a low carbohydrate diet (<42%) or high carbohydrate diet (45% to <50%).

Blinding Used (if applicable):  not applicable

Intervention (if applicable):

  • All patients were seen in OB clinic within 1 wk of diagnosis of GDM
  • Diabetic diet: Kcal: 25-35 kcal/kg prepregnancy DBW, 42% or 45% to 50% carbohydrate.
  • Diabetes educator and dietitian saw all patients.
  • Study participants kept daily diet records, exercise records and monitored daily fasting and 1-hr postprandial glucose after 1 meal/d and well as urinary ketones 3 times/wk.
  • Dietitian reviewed diet records weekly and modified diet when ketones were reported.
  • Insulin initiated in subjects with FBG >105 mg/dl or 1-hr postprandial blood glucose >140 mg/dl when diet adjustment by the dietitian failed to lower blood glucose.
  • HgA1c at baseline and after 6 wk intervention.

Statistical Analysis

Relative risks and 95% confidence intervals were calculated.  Two-tailed Student's t test, corrected chi-square and Fisher exact tests were used when appropriate.

Data Collection Summary:

Timing of Measurements

HgA1c at baseline and after 6 wk intervention.

Dependent Variables:

  • Weight gain
  • HgA1c
  • Mean fasting and 1-hr postprandial capillary glucose
  • Birth weight
  • Macrosomia: birth weight >4000 g
  • C-section for cephalopelvic disproportion or macrosomia
  • Use of insulin

Independent Variables

  • All patients were seen in OB clinic within 1 wk of diagnosis of GDM
  • Diabetic diet: Kcal: 25-35 kcal/kg prepregnancy DBW, 42% or 45% to 50% carbohydrate.
  • Diabetes educator and dietitian saw all patients.
  • Study participants kept daily diet records, exercise records and monitored daily fasting and 1-hr postprandial glucose after 1 meal/d and well as urinary ketones 3 times/wk.
  • Dietitian reviewed diet records weekly and modified diet when ketones were reported.
  • Insulin initiated in subjects with FBG >105 mg/dl or 1-hr postprandial blood glucose >140 mg/dl when diet adjustment by the dietitian failed to lower blood glucose.
  • HgA1c at baseline and after 6 wk intervention.

Control Variables

Description of Actual Data Sample:

Initial N: 

42 women with diet-controlled GDM diagnosed between 24 and 28 wk gestation.

Attrition (final N):  42, 21 in each group

Age:  29.1 +/- 6.3 years in low carbohydrate group, 29.9 +/- 7.2 years in high carbohydrate group 

Ethnicity: 

81% in the low carbohydrate group and 83% in the high carbohydrate group were of Hispanic ethnicity.

Other relevant demographics:

Anthropometrics

Location:  California

Summary of Results:

Means by diet group:
  Carbohydrate
  Low High

Weight gain , lb     

37.6+2.6  39.1+10.8

Birth weight, g

3694+378    3890+453

Other Findings

Diet records documented that those on low carbohydrate diets consumed diets <42% carbohydrate and those on high carbohydrate diets consumed diets between 45% and 50% carbohydrates.

Mean postprandial glucose at 6 wk was significantly lower in the low carbohydrate group (110+18 mg/dL vs. 132+19 mg/dL; P<0.04).

Only 1 subject in the low carbohydrate group required insulin, whereas 7 subjects in the high carbohydrate group (33%) required insulin (RR 0.14; 95% CI, 0.12-1.0; P<0.048)

The incidence of LGA infants was significantly lower in the low carbohydrate group when compared with the high carbohydrate group (9% vs. 42%; P<0.035; RR, 0.22; 95% CI, 0.05-0.091).

Subjects in the high-carbohydrate group had a higher rate of c-sections for cephalopelvic disproportion and macrosomia than subjects in the low carbohydrate group (48% vs. 3%; P<0.037; RR = 0.15; CI=0.04-0.94).

2 patients in the low carbohydrate group experienced ketonuria that was corrected with a change in diet.

There were no significant differences in HgA1c at baseline or after 6 wk on the diet between the low and high carbohydrate diet groups;  however, HgA1c decreased from ~9% to 6.6% to 7.2% after diet intervention.

Author Conclusion:

Carbohydrate restriction in patients with diet-controlled GDM results in improved glycemic control, less need for insulin therapy, a decrease in the incidence of LGA infants, and a decrease in C-sections for cephalopelvic disproportion and macrosomia.

This study did not have the power to determine that there is an absolute lack of perinatal risk associated with carbohydrate restriction, but did have the power to determine that carbohydrate restriction is beneficial in improving postprandial glycemic control, reducing the incidence of LGA infants and c-sections and reducing the need for insulin therapy in patients with diet-controlled GDM.

Funding Source:
University/Hospital: University of California Irvine Medical Center
Reviewer Comments:

There was no indication that glucose meters used by the subjects were checked for accuracy.

No indication that the type of carbohydrate was restricted or monitored (low glycemic vs. high glycemic foods).

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? 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? 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? ???
  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? ???
  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? 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? ???
  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? ???
  7.5. Was the measurement of effect at an appropriate level of precision? ???
  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)? 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