GDM: Medical Nutrition Therapy (2016)


Wolff S, Legarth J, Vangsgaard K, Toubro S, Astrup A. A randomized trial of the effects of dietary counseling on gestational weight gain and glucose metabolism in obese pregnant women. Int J Obes. 2008; 32: 495-501.

PubMed ID: 18227847
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 determine if restriction of gestational weight gain in obese women can be achieved by dietary counseling and whether this restriction could reduce the pregnancy-induced increases in insulin, leptin and glucose.

Inclusion Criteria:
  • Non-diabetic
  • Caucasian
  • Obese (BMI 30 or more)
  • Pregnant women.
Exclusion Criteria:
  • Smokers
  • Younger than 18 years or older than 45 years
  • Multiple pregnancies
  • Medical complications known to affect fetal growth adversely or to contraindicate limitation of weight gain.
Description of Study Protocol:


Researchers recruited from the register of newly diagnosed pregnancies from two hospital systems in Denmark. Researchers consented subjects prior to randomization.


Randomized controlled trial.

Blinding Used

  • Blinding to dietitians during the intervention was not possible 
  • Physicians and midwives were blinded in regard to the treatment assignment
  • Women were asked not to reveal the allocation by the randomization.


The intervention group received 10 one-hour consultations each with a trained dietitian during the pregnancy. Women were instructed to eat a healthy diet according to the official Danish dietary recommendations (fat intake: maximum 30% energy; protein intake 15% to 20% energy; and carbohydrate intake: 50% to 55% energy). The energy intake was restricted based on individually estimated energy requirements (EER) and estimated energetic cost of fetal growth (EER = basal metabolic rate of 1.4). The intervention was designed to restrict the gestational weight gain to 6kg to 7kg.

Statistical Analysis

  • Descriptive analyses of differences between intervention and control group used simple student T-tests and 95% confidence intervals (CIs); dichotomous variables were tested using Chi Square test
  • ANCOVA was used to assess mean differences in weight development between the two groups and the changes in blood parameters with maternal age and parity included as fixed factors, and height and weight at inclusion was included as covariates in the model. For blood parameters, the concentration at inclusion was added as covariate as well. 
  • Group effects on dietary intake were tested using repeated measurements including intake, weight and height at inclusion as covariates and maternal age and parity included as fixed factors in the model. 
Data Collection Summary:

Timing of Measurements

  • Prior to randomization, a self-administered questionnaire was used to assess pre-pregnancy weight
  • Seven-day food records: Inclusion (baseline), 27 weeks and 36 weeks of gestation
  • Height, weight, blood pressure and heart rate were taken at inclusion, 27 and 36 weeks gestation
  • Fasting blood samples and two-hour postprandial samples were taken at inclusion, 27 weeks and 36 weeks gestation
  • Ultrasound at 30, 33 and 36 weeks of gestation in addition to routine clinical schedule
  • Delivery: Infant weight, length, apgar score and head and abdominal circumference; placental weight; delivery method
  • Self-administered questionnaire (timing not mentioned) collected maternal weight development from 36 weeks of gestation until delivery and first, second and third week postpartum
  • Four weeks postpartum: Maternal body weight.

Dependent Variables

  • Daily energy intake (from seven-day food record)
  • Diet composition (from seven-day food record)
  • Weight (fasting with voided bladder and light clothing)
  • Height
  • Blood pressure
  • Heart rate
  • Serum insulin, leptin and blood glucose
  • Fasting blood glucose and blood glucose two hours postprandial to an oral glucose tolerance test of 50g glucose
  • Duration of gestation (via ultrasound scanning of bi-parietal diameter)
  • Birth weight and infant length at delivery
  • Placental weight
  • Apgar score
  • Head and abdominal circumference at birth
  • Pregnancy and birth complications (monitored in mother's hospital journals)
  • Method delivery (mother's hospital journal)
  • Maternal weight development form 36 weeks gestation until delivery
  • Postpartum weight first, second and third weeks (self-report) and fourth week (measured in clinic)
  • Total gestational weight gain (difference between self-reported pre-pregnancy weight and weight just before delivery)
  • Rate of weight gain: Calculated as the difference between the measured weight at inclusion and 36 weeks of gestation divided by the number of weeks from inclusion to 36 weeks of gestation.

Independent Variables

Treatment group:

  • Intervention received 10 consultations of one hour each and restriction designed to cap the weight gain at 6kg to 7kg
  • Control group had no consultations with the dietitian and no restrictions on energy intake or gestational weight gain.

Control Variables

  • All participants were supplied with dietary supplements to ensure a sufficient intake of vitamins and trace elements with special emphasis  on iron and folic acid intake
  • All participants followed the same routine clinical schedule with additional ultrasound measurement of fetal growth at 30, 33 and 36 weeks of gestation.
Description of Actual Data Sample:

Initial N

73 pregnant women.

Attrition (final N):


  • Seven developed conditions that made them ineligible for continued participation [one spontaneous abortion, one twin pregnancy, one continued smoking, two bedridden from early pregnancy (fibromyalgia, pelvic pain), two diagnosed GDM at inclusion]
  • 13 dropped out early in the trial mainly due to lack of time to participate in a time-consuming trial or disappointment at being randomized to the control group
    • Five dropouts from intervention
    • Eight dropouts from control and three additional people were diagnosed with GDM during pregnancy and were offered gestational diabetes diet (excluded from results except for reports on the incidence of GDM).


  • Intervention: 28±4 years for intervention
  • Control: 30±5 years for control (P=0.069).

Other Relevant Demographics

Recruited early in pregnancy (15±3 weeks of gestation).


Women who dropped out did not differ in characteristics from the participating women; there were no significant differences between two groups for baseline characteristics.




Summary of Results:

Key Findings

  • The women in the intervention group successfully limited their energy intake and followed the dietary instructions for the recommended macronutrient composition of the diet. Fat energy and carbohydrate percentages decreased and protein percentage energy intake increased in the intervention group compared to the control groups.
  • Intervention group restricted their total gestational weight gain to an average of 6.6kg±5.5kg, compared to a gain of 13.3kg±7.5kg in the control group (mean difference of 6.7kg, 95% CI of the difference 2.6kg to 10.8kg, P=0.002).
  • The average weekly weight gain from inclusion to 36 weeks gestation was significantly reduced by 0.18kg per week (0.07 to 0.30, P=0.02) in the intervention group compared to the control group (0.26kg±0.15kg vs. 0.44kg±0.21kg per week)
  • The intervention group retained 6.9kg less weight than the control group four weeks postpartum (4.5kg vs. 2.4kg, 95% CI of difference: 2.5 to 11.2, P=0.003) compared to the pregnancy weight.

Other Findings

  • The weight gain until 36 weeks gestation was highly correlated to total gestational weight gain (R2=0.73, P<0.001) and associated only by initial height and group allocation, which together explained 36% of variation in weight gain (group: P=0.002, height: P=0.04)
  • There were no group differences in weight gain from self-reported pregnancy weight to inclusion or in the spontaneous weight loss by giving birth
  • The restriction of gestational weight gain in the intervention group reduced the increment in both insulin and leptin by 20% compared to control group at 27 weeks gestation. The insulin was further reduced by 23% at 36 weeks gestation (no additional effect for leptin). 
  • The fasting glucose concentration in the control group had a small decrease with advancing gestational age (-0.04mmol per L at 27 weeks and -0.1mmol per L at 36 weeks). The intervention showed no reduction of fasting glucose at 27 weeks but at 36 weeks there was an 8% reduction, P=0.03). No differences between groups for the two-hour glucose concentration after OGTT at 27 and 36 weeks gestation. 
  • Researchers conclude it is beyond the scope of the study to investigate an impact of weight restriction on fetal growth. The intervention group did not have any detectable adverse effects on fetal growth; fewer incidences of pregnancy and birth complications were observed.
Author Conclusion:

This study demonstrates it is possible to restrict the gestational weight gain in obese women by a dietary intervention that aimed to restrict the energy intake and provide a macronutrient composition of the diet consistent with the official Danish dietary recommendations. The restriction reduces the deterioration in the glucose metabolism.

Funding Source:
DesireeĀ“and Niels Yde Foundation
In-Kind support reported by Industry: Yes
Reviewer Comments:

 Pharma Vinci provided vitamins only (in-kind industry support).

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? No
  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)? No
  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? No
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