GDM: Prevention of GDM Diagnosis (2008)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To investigate relationships between dietary macronutrient intake and glucose tolerance in pregnancy.
Inclusion Criteria:
  • nulliparious women
  • screened for GDM at 24-28 weeks of gestational age - calculated from date of last menses, and most pregnant women had an ultrasound examination at the first trimester to confirm the age of gestation. 
  • completion of 24 hour dietary assessment - subjects were interviewed by dietitians trained in assessing usual food patterns. Dietitians constructed a list of the amounts of foods consumed, which were entered into a software program (Zhong Wen Haung, Shanghai Medical University,1998) containing the Chinese nutrient data base (Nutritional Evaluation and Dietary Prescription for Pregnant Women). 
  • The study was approved by by the Human Ethics Committee of the University of Wollongong and by the Director of the International Peace Maternity and Child Health Hospital of China Welfare Institute.
Exclusion Criteria:
Exclusion criteria was not delineated.
Description of Study Protocol:

Recruitment : Subject selection was based on a sequential screening of hospital records from 1996 and Sept 1998.

Design:Case control

Blinding used:  not applicable 

Intervention:  not applicable

Statistical Analysis :

  • relationships between dietary variables and diagnostic categories were assessed initially by 1 way ANOVA in the complete data set and also in a subset weighing 60-80 kg who were matched between categories for age, height, and BMI
  • differences between groups were localized using Schefffe's post hoc test
  • selected relationships were further examined using either ordinal logistic regression, with diagnostic category the dependent variable (NGT=0, IGT=1, GDM=2) and individual dietary variables with either body weight or BMI as independent variables, or by partial correlation analysis of the natural logarithm of the areas under the glucose curve during the OGTT against body weight and dietary intake measures
  • all analyses were performed using JMP software (version 3.1.6.2, SAS Institute, Cary (NC)
  • all summary data are means±SEM.

 

 

Data Collection Summary:

Timing of Measurements

  • Height and weight were measured at the time of the screening

Dependent Variables

  • NGT
  • IGT - individuals were categorized as having IGT if only one venous plasma glucose concentration met or exceeded these values-fasting 5.8 mmol/L; 1 h, 10.6 mmol/L ; 2 h, 9.2 mmol/L; and 3-h, 8.1 mmol/L .  
  • Gestational Diabetes Mellitus (GDM) - based on the recommendations of national Diabetes Data Group and involved a standard screening test  for GDM using the 50-g 1-h oral glucose challenge. GDM was diagnosed if >= 2 venous plasma glucose concentrations met or exceeded the following values: fasting 5.8 mmol/L; 1 h, 10.6 mmol/L ; 2 h, 9.2 mmol/L; and 3-h, 8.1 mmol/L . 

Independent Variables

  • BMI(kg/m2)
  • Total energy (kcal)- fat (% kcal), protein (% kcal), carbohydrate (% kcal)
  • Fat profile (% total fat) - polyunsaturated, monounsaturated, saturated
  • Fat profile (% total kcal) - polyunsaturated, monounsaturated, saturated
  • Fat profile (kcal) - polyunsaturated, monounsaturated, saturated
  • P:S ratio
  • Fiber (g)

Control Variables

 

Description of Actual Data Sample:

Initial N: 171

Attrition (final N):  171

Age: not defined/reference was made to 'age bands' in methods section.

Ethnicity: Chinese

Other relevant demographics:

Anthropometrics

Location: University of Wollongong, Wollongong, New South Wales, Australia

 

Summary of Results:

The three groups of subjects were well matched with respect to age, gestational age, and height; however IGT and GDM subjects were significantly heavier than the normal group (Table1).

Table 1 Nutritional data obtained by 24-h recall dietary assessment for pregnant women with NGT, IGT, and GDM

 

  >>All >> Subjects>> (n=171) >>BMI- matched (n=116>
 

Normal

IGT

GDM

Normal

IGT

GDM

n

77

38

56

47

26

43

BMI (kg/m2)

24.2±0.31

25.7±0.5*

26.4±0.4*

25.4±0.3

26.1±0.4

26.2±0.4

Total energy(kcal)

 2,133±42

 2,223±75

 2,134±61

 2,135±54

 2,304±99

 2,156±72

Fat (%kcal)

 32.4±0.8

 30.6±1.0

 30.0±1.0

 33.2±1.2

 30.4±1.3

 29.1±1.3*

Protein (%kcal)

 16.3±0.3

 17.2±0.5

 16.2±0.4

 16.4±0.4

 17.1±0.7

 16.3±0.5

Carbohydrate (% total kcal)

 51.7±0.9

 52.3±1.3

 53.8±1.2

 51.1±1.2

 52.6±1.6

 54.6±1.5

Fat profile (%total fat)  -  -  -  -  -  -
Polyunsaturated

 31.6±0.7

 29.5±1.0

 28.2±0.9*

 31.7±0.9

 30.0±1.2

 28.1±1.0*

Monounsaturated

 26.3±0.6

 28.8±1.0

 25.7±0.8

 27.2±0.8

 28.1±1.2

 26.0±0.9

Saturated

 42.1±1.0

 41.8±1.6

 46.1±1.4*

 41.1±1.3

 41.9±1.9

 45.9±1.3*

Fat profile (kcal)  -  -  -  -  -  -
Polyunsaturated  10.2±0.3  8.9±0.4  8.5±0.4*  10.5±0.5  9.0±0.5  8.2±0.5*
Monounsaturated

 8.6±0.3

 8.7±0.4

 7.8±0.4

 9.1±0.5

 8.4±0.5

 7.6±0.4*

Saturated

 13.7±0.5

 13.0±0.8

 13.8±0.6

 13.7±0.7

 13.0±1.0

 13.3±0.7

Fat profile (kcal)

-

-

 -

 -

Polyunsaturated

218±8.9

195±9.2

177±8.4*

227±13.1

204±11.7

173±9.6*

Monounsaturated

182±7.7

192±10.2

163±8.6

194±10.9

193±12.5

162±9.5

Saturated

291±11.3

288±22.2

291±14.1

291±14.8

297±28.9

282±13.6

P:S ratio

 0.81±0.04

 0.77±0.05

 0.67±0.04*

 0.83±0.05

 0.77±0.06

 0.65±0.04*

Other nutrients

 -

 -

 -

 -

 -

 -

Fiber (g)

 14.1±0.8

 14.4±1.3

 13.2±0.7

 13.5±1.0

 15.7±1.7

 13.4±0.8

Data are n or means ± SEM. *Significantly different from NGT pregnant group (Scheffes F Test, (<0.05); ¶ significant effect across all groups by analysis of variance( P<0.05).

Other Findings

Polyunsaturated fat intake had no apparent effect on the low incidence of abnormal glucose tolerance in the lowest body weight tertile, but was negatively associated with abnormal glucose in the higher body weight tertiles.

Author Conclusion:
  • Increased polyunsaturated fat intake was associated with a reduced incidence of glucose intolerance during pregnancy.
  • The dietary methodology had been validated in previous research compairing interview data with weighted food records conducted in the homes of the subjects.
  • Reliability of the method was also assessed by conducting repeat interviews with one-third of the sample and comparing results.
  • The study did not suffer from many of the measurement problems associated with dietary studies in other settings, largely because there was less variation in the food supply and traditional eating patterns were still the norm.

Limitation

  • Food variations on the weekend was less likely to be detected.
Funding Source:
Government: Australia Chinese Links Program
Reviewer Comments:

The noted limitation and critique of the study , as stated by the authors appear to be very appropriate.

Case control studies are studies in which patients who already have a certain condition are compared with people who do not. Case control studies are less reliable than cohort studies. Just because there is a statistical relationship between two conditions does not mean that one condition actually caused the other.

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? ???
  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? ???
  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.) ???
  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? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  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%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? N/A
  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? N/A
  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? N/A
  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? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  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? ???
  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? N/A
  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? ???
  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? N/A
  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? ???
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? ???