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ORP: Nutrition Prescription for Gestational Weight Gain (2014)

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

To determine if a low glycemic index diet in pregnancy could reduce the incidence of macrosomia in an at-risk group (women in second pregnancies who had previously delivered an infant weighing greater than 4,000g).

Inclusion Criteria:
  • Secundigravid women
  • Previous delivery of macrosomic infant weighing more than 4kg
  • Informed consent.
Exclusion Criteria:
  • Underlying medical disorders, including previous history of gestational diabetes
  • Women on drugs
  • Those unable to give full informed consent
  • Less than 18 years old
  • Gestation greater than 18 weeks
  • Multiple pregnancy.
Description of Study Protocol:

Recruitment

All women meeting inclusion criteria were identified on first contact with the hospital and recruited at first antenatal consultation. 

Design

Randomized controlled trial.

Blinding Used

Not used except for sonographers; authors note limitation of the Hawthorne effect. There were no imposed rules to women in the control arm introducing some elements of dietary modifications themselves.  

Intervention

  • Women in the control arm received routine antenatal care (no formal dietary advice or specific advise about gestational weight gain). Women in intervention group attended one dietary education session lasting two hours in groups of two to six women with the research dietitian. Women were advised on general healthy eating guidelines for pregnancy, following the food pyramid. The rest of the education was on the glycemic index (definition, concept and rationale for use in pregnancy). Women were encouraged to choose as many low glycemic index foods as possible and exchange high glycemic index carbohydrates for low glycemic index alternatives. Women received written resources about low glycemic index foods after the session.
  • Low glycemic index diet was eucaloric
  • Research dietitian met with patients at 28 weeks and 24 weeks gestation to reinforce diet and answer questions. 

Statistical Analysis

  • Independent samples T-test was used to compare means within groups of patients for the primary outcome of birth weight. Chi square tests compared categorical variables between groups. Weight gain was assessed in:
    • An independent samples T-test on amount of weight gain
    • On the basis of a linear model examining total weight with control for starting weight.
  • Statistical significance was set at P<0.05. 
Data Collection Summary:

Timing of Measurements

  • First antenatal consult:
    • Weight, height, body mass index calculated
    • Fasting blood glucose
    • Mid-upper arm circumference 
    • Demographic data collected (including socioeconomic)
    • Smoking history
    • Three-day food record: Estimate glycemic load (repeated in second and third trimesters of pregnancy but no specific weeks provided).
  • Each antenatal consultation following the first: Maternal weight
  • 28 weeks gestation:
    • Fasting blood glucose
    • Glucose challenge test one hour after 50g glucose load.
  • 34 weeks gestation:
    • Fetal biometry ultrasonography: Fetal anterior abdominal wall width (marker of fetal adiposity)
    • Questionnaire to assess low glycemic index diet adherence (intervention group only).
  • Delivery:
    • Infant birth weight, length, head circumference
    • Calculated ponderal index 
    • Birthweight percentiles.

Dependent Variables

  • Birth weight at delivery: Weight of the infant
  • Mean birthweight percentile: Corrected for maternal weight, height, parity, ethnicity, gestational age at delivery and infant sex (Gestation Network's Bulk Calculator, version 6.2.3 UK)
  • Birthweight adjusted for maternal body mass index
  • Ponderal index (100 x mass in g per height in cm3)
  • Incidence of fetal macrosomia (greater than 4kg)
  • Women's gestational weight gain (weight at delivery minus weight pre-pregnancy)
  • Glucose challenge test results (one hour after 50g glucose load)
  • Fasting blood glucose
  • Incidence of gestational diabetes according to Carpenter and Coustan criteria and the American Diabetes Association criteria
  • Cord blood glucose
  • Dietary glycemic index (estimated from food records)
  • Mean glycemic load (estimated from food records)
  • Energy intake (estimated from food records)
  • Cesarean delivery rate, labor induction rate, other maternal complications.

Independent Variables

Intervention or control group.

Control Variables

All women who had a glucose challenge test result of 8.3mmol per L or higher had formal glucose tolerance testing and if gestational diabetes was diagnosed, care continued in the multi-disciplinary diabetes clinic.

Description of Actual Data Sample:
  • Initial N: 909 were contacted as meeting inclusion criteria; 851 agreed to meet with researcher. 51 women met exclusion criteria or miscarried before randomization; 800 were randomized.
  • Attrition (final N): 800; one stillbirth occurred in the intervention arm (at 39 weeks). Only 781 women were represented in the baseline demographics of the control and intervention groups (intervention 383; control 398).
  • Age: 32±4.2 years
  • Other relevant demographics: Gestational age at recruitment was 13.0±2.3 weeks; the percentage of smokers was 17±4 for the intervention group and 12±3 for the control group
  • Anthropometrics: Groups were the same for BMI (26.8±5) and fasting glucose (4.5mmol per L average) as well as previous birth weight
  • Location: Dublin, Ireland.
Summary of Results:

Key Findings

  • No significant difference between the two groups in birth weight at delivery or mean birthweight percentile, birthweight adjusted for material BMI, gestation at delivery, infant's sex or ponderal index at birth
  • Fetal macrosomia recurred in 189 (51%) of the intervention group and 199 (51%) of the control group; P>0.05.

Other Findings

  • Women who received dietary intervention had significantly less gestational weight gain than those in the control group. At 40 weeks' gestation, the mean gestational weight gain in the intervention group was 12.2kg compared with 13.7kg in the control (mean different -1.3, 95% CI: -2.4 to -0.2; P=0.01). The difference persisted when initial weight with regression analysis was used (mean difference -0.7, 95% CI: -1.3 to -0.13; P=0.018).
  • Women in the intervention were less likely to exceed gestational weight gain recommendations as outlined by the IOM (38% vs. 48%; P=0.01). Among women with a normal BMI (18.5 to 24.9), 26% of controls exceeded the guidelines compared with 15% of the intervention group (P=0.02). In overweight women (BMI 25 to 29.9), 67% of controls and 53% of intervention exceeded the guidelines (P=0.02). Women with a BMI higher than 30 did not differ for gestational weight gain (P=0.8).
  • More women in the control group had a glucose challenge test result of more than 7.8mmol per L at 28 weeks gestation as well as fasting glucose of more than 5.1mmol per L
  • An equal number of women in each group had formal glucose tolerance testing and did not differ in incidence of gestational diabetes. Cord blood glucose was the same between the two groups.
  • No differences in dietary glycemic index between groups existed prior to intervention. After the initial nutrition education, the intervention group had a lower glycemic index in the second trimester (56.1±4.0 vs. 57.8±3.7; mean difference -1.7, 95% CI: -2.2 to -1.1; P<0.001). This same trend is noted for glycemic load at randomization and during the second trimester (124.1±32.5 vs. 140.0±36.3; mean difference -15.9, 95% CI: -20.8 to -10.9; P<0.001) and third trimester (P<0.001). 
  • The groups were not different on energy intake at baseline. In the second and third trimester, the intervention group had lower energy intake (P<0.01). The intervention group had higher intakes of fiber in the third trimester. 
  • Almost 80% of the intervention women reported following the low glycemic index dietary advice either all or most of the time
  • No significant differences in the rate of cesarean delivery. Women in the intervention delivered at a later gestation age than those in the control group (P=0.017). Women in the intervention group were more likely to have their labor induced than controls (18% vs. 11%, P=0.012). No differences between groups for other measured complications.
  • Pre-term deliveries (less than 37 weeks) and shoulder dystocia did not differ statistically between groups. 

 

Author Conclusion:

The authors found that a low glycemic index diet in pregnancy had no effect on infants’ birth weight in a group at risk of fetal macrosomia. It did, however, have a significant positive effect on gestational weight gain and on maternal glucose intolerance.

Funding Source:
Government: Health Research Board of Ireland
University/Hospital: National Maternity Hospital Medical Fund
Reviewer Comments:
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? No
  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? No
  4.4. Were reasons for withdrawals similar across groups? No
  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? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  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)? 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? 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