GDM: Carbohydrate (2016)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To evaluate the impact of energy and macronutrient intake on infant birthweight in women with gestational diabetes undergoing intensive management.
Inclusion Criteria:
  • Women screened via oral glucose tolerance test between 24th and 28th weeks of gestation
  • Gestational diabetes or gestational mild hyperglycemia diagnosis
Exclusion Criteria:

Not explicitly stated, but participants were excluded for the following reasons:

  • Treated hypertension
  • Asthma

 

Description of Study Protocol:

Recruitment

1 out of every 4 women participating in a wider prospective study conducted from Jan 1993 to December 1993 in 15 maternity hospitals in northern France were selected to be a part of the nutrition survey.

Design:  Longitudinal Study   

Blinding used (if applicable):  not applicable

Intervention (if applicable) 

This study was ancillary to the following larger study:

  • Intervention for parent study was intensive monitoring by a dietitian and endocrinologist. Patients were seen weekly during the first month then every 2 weeks until delivery. 
  • At each visit, fasting and 2-hr postporandial serum glucose, dietary adherence , weight changes, and blood pressure were evaluated.  Self monitoring included urine analysis for ketones 3 times/day and blood glucose 4 times/day.
  • Energy content of prescribed diet was based on prepregnancy BMI< prediagnostic weight gain, and energy intake evaluated by 3-month diet history. Prescription >=1800kcal/day
  • 50-55% carbohydrate, 30-35% fat, 10-15%protein
  • Insulin prescribed as needed

 Statistical Analysis

  • Univariate analyses using nonparametric tests - Spearman correlations, Wilcoxon
  • Forward stepwise regression analyses -  effect of maternal age, smoking, parity, prepregnancy BMI, pregnancy weight gain, infant sex, gestational duration, insulin therapy, fasting and 2-hour  postprandial serum glucose, and energy and macronutrient intake on infant birthweight
Data Collection Summary:

Timing of Measurements

  • Screening between 24-34 weeks of gestation
  • Patients seen weekly for the first month and bi-weekly thereafter until delivery

Dependent Variables

  • Birthweight
  • Compared to growth curves for the French populations (AUDIPOG study):

              -large-for gestational-age (LGA) when birthweight > 90th percentile

              - small-for-gestational-age (SGA) birthweight < 10 th percentile

Independent Variables

  • Baseline Diet - first interview used 3-month diet history adapted from Burke
  • Diet during intervention period - Mean of two 3-day food records (2 weekdays and 1 weekend day) during the 3rd and 7th weeks of follow-up.  Data were checked by a dietitan in each study center, and nutrient intake was calcualted using a Frendch food composition table after coding by two trained dietitians

Control Variables

  • Maternal age
  • Smoking
  • Gestational age - last menstrual period and early ultrasonographic assessment
  • Prepregnancy BMI - self-report measured at the first exam
  • Mean fasting serum glucose/2-hr postprandial glucose-average of all values determined at each visit during treatment
  • Parity
  • Pregnancy weight gain
  • Infant sex
  • Gestational duration
  • Insulin therapy
Description of Actual Data Sample:

Initial N: 99

Attrition (final N): 80

  • 1 premature birth
  • 18 diet underreporters, defined as reported Energy intake/basal metabolic rate (BMR) ratio <1.14 : BMR estimated using Schofield's equations using age, sex, and weight

Age: 30.2±5.3 (mean±sd) years

Ethnicity: French, not further specified

Other relevant demographics:

  • 66% multiparous
  • 16% smoked during pregnancy

Anthropometrics Prepregnancy BMI: 25.2±5.2 (mean±sd)

Location: 15 maternity hospitals in northern France

 

Summary of Results:

 

Variables

Standardized regression coefficient (n=73)

R^2=0.27

p value

Gestational duration, wk

0.34

0.002

Smoking

 -0.27

 .01

Carbohydrate, g/d

 -0.24

 0.03

 Other Findings

  • 61% GDM; 39% mild hyperglycemia
  • Birthweight: 3402±438 (mean±sd) kg; 16% LGA, 4% SGA
  • 39% babies female
  • Gestation duration: 39.3±1.2 (mean±sd)
  • 24% (n=19) had a carbohydrate had carbohydrate intake lower than the prescribed level by at least 20%

 

Author Conclusion:
Birthweight is directly related to gestational age and inversely related to smoking.  The macronutrient composition of the diet affects the outcome of pregnancy in women with carbohydrate intolerance during pregnancy.  Infant birthweight is inversely related to carbohydrate intake.  This relationship is independent of the other factors and is still present when accounting for insulin therapy.
Funding Source:
Government: Conseil Regional Nord CPAM
Industry:
Novo Nordisk, Lifescan, Servier, Becton-Dickinson, Nestle, guigoz, Lipha, Lilly, Merck-Clevenot, Roche, Schering
Food Company:
Pharmaceutical/Dietary Supplement Company:
Other:
Reviewer Comments:
  • Eligibility criteria not explicitly stated
  • Unclear how the "1 in 4" participants selected from parent study; results said participants in sub-study were of higher SES compared to overall sample
  • Effect measures inadequate: Since diet was measured as part of an intervention to encourage 50-55% kcal from carbohydrate, better compliers with overall intervention may have had higher carbohydrate intake, thereby results of study could be due to factors other than higher carbohydrate diet
  • Carbohydrate has smaller effect than smoking; are smaller babies healthier babies?  Goal is to prevent macrosomia, not encourage low birth weight
  • Could have presented results with and without "underreporters" as macronutrient composition may have been accurately reported
  • Limitations not described adequately: i.e. measurement error of diet, uncertainty regarding whether finding was due to better compliance to other intervention factors or adherence to dietary recommendations; Statement that "careful distribution of carbohydrates and use of low glycemic index foods helping in limiting postprandial hyperglycemia" was not tested in this intervention
  • Study supported by many industry groups, including Novo Nordisk, lily, Nestle, Roche, Schering
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? ???
  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? ???
  2.2. Were criteria applied equally to all study groups? ???
  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? No
3. Were study groups comparable? N/A
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  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? 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? N/A
  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.) N/A
  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? 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? N/A
  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? N/A
  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? No
  7.1. Were primary and secondary endpoints described and relevant to the question? No
  7.2. Were nutrition measures appropriate to question and outcomes of concern? No
  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? No
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? No
10. Is bias due to study's funding or sponsorship unlikely? ???
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? ???