GDM: Carbohydrate (2016)

Perichart-Perera O, Balas-Nakash M, Rodriguez-Cano A. Legorreta-Legorreta J, Parra-Covarrubias A, Vadillo-Ortega F. Low glycemic index carbohydrates versus all types of carbohydrates for treating diabetes in pregnancy: A randomized clinical trial to evaluate the effect of glycemic control. International Journal of Endocrinology. 2012; 2012: 296017. PubMed ID: 23251152
Study Design:
Randomized Controlled Trial
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To compare the effect of including only low glycemic index (GI) carbohydrates (CHO) in the diet against all types of CHO on maternal glycemic control and on the maternal and newborn's nutritional status of women with type 2 diabetes and gestational diabetes mellitus (GDM). 
Inclusion Criteria:
  • Women
  • A gestational age of 29 weeks or more
  • GDM or pre-gestational type 2 diabetes mellitus
  • Planned to attend their pregnancy at the institution conducting the research.
Exclusion Criteria:
  • Women
  • Type 1 diabetes mellitus
  • Renal, hepatic or other metabolic diseases
  • Unable to follow the nutrition intervention. 
Description of Study Protocol:


Women had an initial visit to evaluate suitability, then were invited to participate and provided informed consent.


  • For this blinded RCT, a clinical dietitian randomly assigned subjects to one of two nutrition intervention groups.
    • Group One included all types of CHO, following American Dietetic Association guidelines, with the subjects received an individual food plan based on CHO restriction (40% to 45% total energy intake) using a basic CHO-counting strategy. Calorie and CHO prescriptions were revised at every visit and changes made according to weight gain and presence of ketonuria. Fat intake recommendation was less than 40% of intake and protein recommendation was 20% to 25% of intake.
    • Group Two received the same intervention as Group One but were advised to eliminate all moderate and high-GI foods (GI higher than 55). Both groups received the same individual nutrition education at each visit, following a specific protocol for this study.
  • All subjects performed glucose self-monitoring before and two hours after meals, six times a day on two days of the week. At each visit subjects reviewed their glucose monitoring records with the dietitian, identifying glucose values out of range and relating them with food intake.
  • Subjects were followed up every two to three weeks until the end of pregnancy. At each visit nutrition assessment was done and recommendations made accordingly. Diet adherence was measured as the mean energy intake adequacy throughout the intervention, calculated based on the energy intake reported each visit and the energy intake recommendation from the previous visit. 

Blinding Used

Obstetricians, endocrinologists and lab personnel were not aware of the study groups.


Both groups followed AND nutrition practice guidelines and received the same individual nutrition education, except:

  • Group One included all types of CHO, regardless of GI
  • Group Two excluded all moderate and high-GI foods (GI higher than 55).

Statistical Analysis

  • ANOVA was used to assess intra- and inter-group differences
  • Multiple logistic regression was used with type of DM and study group as factors
  • Multiple logistic regression was used with type of DM and study groups as independent variables and excessive maternal weight gain as dependent variable
  • Multiple logistic regression models was used for evaluating risk of adverse clinical outcomes; type of DM, study group, presence of infection during pregnancy; and infection during pregnancy were independent variables and clinical adverse outcomes were dependent variables.
Data Collection Summary:

Timing of Measurements

  • Fasting plasma glucose levels measured every two weeks by glucose oxidase method
  • Weight was measured at each visit; pre-gestational weight was self-reported
  • Diet was measured at baseline and every month (every two sessions) by the dietitian using the 24-hour recall method
  • Subjects collected the first morning urine sample the day of each visit to test for ketones.

Dependent Variables

  • Maternal blood glucose control
  • Maternal weight gain
  • Maternal ketonuria
  • Newborn nutritional status (birth weight, length, head circumference per WHO reference data). 

Independent Variables

Low GI CHO (CHO-containing foods with GI less than 55). 

Control Variables

Standard AND nutrition guidelines, including all types of CHO.
Description of Actual Data Sample:

Initial N

N=107 women.

Attrition (Final N)

  • Group One: N=32 women who completed the intervention
  • Group Two: N=41 women who completed the intervention.


  • Mean age: 32±5 years
  • Group One: Mean age of 31.8±5.3 years
  • Group Two: Mean age of 32.3±4.8 years.

Other Relevant Demographics

  • A total of 55 women had type 2 diabetes and 52 women had GDM
  • Mean for type 2 diabetes was 3.75+2.33 years for Group One, 3.71+2.49 years for Group Two
  • The mean gestational age at baseline was 22±6 weeks
  • A total of 32 women in Group One were insulin users at baseline and 34 women in Group Two were insulin users at baseline
  • Of women with type 2 diabetes in Group One, 17 were using oral hypoglycemic agents before pregnancy; of women with type 2 diabetes in Group Two, 24 were using oral hypoglycemic agents before pregnancy
  • At baseline, the glycemic index of diet for Group One was 50.0±8.9 and for Group Two, 51.2±7.2. 


  • Mean weight:
    • Group One: 73.95±16.59kg
    • Group Two: 74.12±13.72kg.
  • Mean height:
    • Group One: 152.36±6.92cm
    • Group Two: 155.28±5.17cm.
  • Pre-gestational BMI:
    • Group One: 32.0±6.3
    • Group Two: 30.5±5.2
  • Overweight or obese:
    • Group One: N=43 (93.5%)
    • Group Two: N=53 (86.8%).


Mexico City, Mexico.


Summary of Results:

Key Findings

  • Fasting plasma glucose decreased significantly in Group One and Group Two throughout the intervention (P<0.003 and P<0.004, respectively) but no significant differences were observed between groups
  • At the end of the intervention, the proportion of women who achieved glycemic goals at different mealtimes was similar between groups (P>0.44)
  • No differences in fasting or capillary glucose throughout the intervention were observed between women who started the intervention earlier (less than 23 weeks of gestation) and women who started later. The proportion of women achieving glycemic goals at the end of pregnancy was also similar, regardless of the number of visits.
  • Regardless of the type of DM, a lower proportion of women in Group Two (9.8%, N=6) was classified as having excessive weight gain compared to women in Group One (34.8%, N=16) (P=0.002)
  • There was a significant decrease in the GI of the diet throughout the intervention period only in Group Two (51.29±7.28 to 47.18±6.93, P=0.001). No other significant dietary differences were observed between groups.
  • A trend for lower birthweight among newborns in Group Two was observed (P=0.06).
  • Multivariate analysis showed the same risk of pre-eclampsia, intrauterine and neonatal death in women from both study groups but a higher risk of prematurity in women in Group Two (P=0.03).
Author Conclusion:
Inclusion of low GI CHO as part of a comprehensive nutrition intervention was equally effective in improving glycemic control as compared to all types of CHO, without differences between pregnant women with type 2 diabetes and women with GDM. The low GI strategy had a positive effect in preventing excessive maternal weight gain but women in this group had higher risk of pre-term birth. More data is needed before recommending restricting high and moderate GI foods for treating diabetes in pregnancy as a better strategy than including all types of CHO. 
Funding Source:
Other: not specified by authors.
Reviewer Comments:
The authors discuss several limitations to this study. Bias may have been introduced by participants because capillary glucose concentrations were self-recorded. Because women received dietary and self-monitoring recommendations during the first prenatal visit, the first glucose value was already a result of the dietary intervention. Also, a systematic error was introduced in the calculation of the diet GI due to lack of GI data of some Mexican foods and food combinations. The 24-hour dietary recall used during visits has limitations, including relying on the patient's memory, not evaluating usual energy and macronutrient intake and the possibility of falsely reporting compliance with the intervention guidelines during an ongoing nutrition education process.
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? Yes
  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? Yes
  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? 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? 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)? 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? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? Yes
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