GDM: Prevention of GDM Diagnosis (2008)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
The purpose of this case control study was to investigate the relationship betwen life-style habits and glucose abnormalities in Caucasian women with and without conventional risk factors for gestational diabetes.
Inclusion Criteria:

A total of 26 women with GDM and 84 women with abnormal value of OGTT were identified. During the first month of this period (April 1999-November 2000), all consecutive subjects with normal glucose tolerance results (294 women) were considered as control subjects.

All participants gave their informed conscent and all procedures were in accordance with the Helsinki Declaration of 1975.

Exclusion Criteria:
Pregnant women known to have diabetes mellitus or a disease affecting glucose metabolism were excluded.
Description of Study Protocol:

Recruitment :

The study included all consecutive women screened from April 1999-November 2000. All pregnant women attending the Department of Obstetrics and Gynecology of the University of Torino (Turin, Italy) are routinely screened with a 50-g oral glucose tolerance test (OGTT) at 24-28 wk of gestational age (as calculated by ultrasound examinations performed during the first trimester of gestation). All patients with a positive screening result(1-h serum glucose concentration >=7.8 mmol/l underwent a 3-h OGTT with 100 g glucose after 1 to 2 weeks.

The test was done in the morning after an overnight fast of at least 8 h but not more than 14 h and after at least 3 days of an unrestricted diet (>= 150 g carbohydrates/day) and exercise, using cut-off values previously proposed for extrapolation of the whole blood glucose values to plasma or serum glucose concentrations.

GDM was diagnosed when two serum glucose values were above the following levels: 5.3 mmol/l after fasting, 10.0 mmol/l at 1 h, 8.6 mmol/l at 2 h, or 7.8 mmol/l at 3 h according to established criteria . The category one abnormal value on the OGTT was defined when just one glucose value was higher than the noted cutoff levels.

Design Case control

Blinding used :

Dietetic interviews were performed by 3 physicians who were trained in assessing habitual food patterns and blinded to the results of the OGTT; other physicians communicated the results of the OGTT to patients after the dietary interview. 

Intervention (if applicable):  not applicable 

Statistical Analysis :

  • Analysis of variance and chi-square test were used to compare means for continous variables or frequencies for discrete variables.
  • ANCOVA (analysis of covariance )were used to compare different continous variables, using BMI as a covariate.
  • Linear correlations were performed to evaluate the association of BMI with dietary variables.
  • Multiple regression analyses were performed to analyse correlations between the polyunsaturated -to-saturated (P:S) fat ratio and fasting insulin, and correlations fibre intake and presence of IGT/GDM, after multiple adjustments.
  • Multiple logistic regression analysis based on the maximum likelihood method was performed to determine the independent contribution of BMI, height, age, familial diabetes and percentage of total, saturated, monounsaturated and polyunsaturated fat on the presence of IGT and GDM.
  • As insulin values were not normally distributed, they were log-transformed.
  • Data are presented as mean±standard deviation or percentages and as odds ratios (OR) and 95% Confidence Intervals.
  • A p value of less than 0.05 was considered significant.

 

Data Collection Summary:

Timing of Measurements: Height was measured at the time of screening. No other timing of measurement were identified.

Dependent Variables

  • Age
  • Height
  • Familial diabetes
  • Classes of BMI -Overweight and obesity were defined as BMI of 25 kg/m2 or more and less than 30 kg/m2 and a BMI of 30 kg/m2  or more, respectively.
  • Saturated fat (% of total fat)
  • Polyunsaturated fat (% of total fat)

Independent Variables

 Clinical Characteristics:

  • Age (years) - conventional risk factor for gestational diabetes, age higher than 35 years.
  • Weight (kg)
  • Height (m) - measured at the time of screening
  • BMI (kg/m2) - the body mass index  was calculated as pre-pregnancy weight in kilograms divided by the square of the height in meters.
  • Nulliparous (%)
  • Smoking (%) - number of cigarettes a day; years of smoking were recorded
  • Alcohol intake - mean daily and weekly alcohol intake and kinds of beverages were obtained by interview.
  • Familial diabetes (%) - first degree relative with Type II (non-insulin-dependent)diabetes mellitus
  • Physical activity (%): light; moderate; vigorous- Usual physical activity during both work and leisure was evaluated.  Arbitrary scores were assigned to degrees of physical activity during work (not working=0, mainly sitting=1, sitting or standing=2, walking/handling materials=3) and leisure (inactive =1 , 4 h a week of physical activity=2, regular physical activity=3). The sum of the two scores was combined and three levels of physical activity were considered: Vigorous (score 5-6), moderate (score 3-4), light (score 1-2).
  • Serum glucose was measured by the glucose oxidase method (Glucose-Analyzer II Beckman, Fullerton, Calif, USA).
  • Fasting Insulin (pmol/l) - was measured by radioimmunoassay (Corning Kit, Modifield, Mass, USA) ; the coefficients of variation were 3.4-5.1 %.

Dietary Data:

Detailed dietetic interviews were performed with all patients by means of a semiquantitative food-frequency questionnaire adapted from Willett and Coll (1985) with the following considerations:

  • subjects were European
  • searched for diet influences on the occurence of gestational hyperglycemia that was closely related to a short-lasting event pregnancy, and different from chronic conditions
  • an evaluation of dietary intake in the previous years was meaningless because women frequently change their dietary habits in pregnancy (more "healthy habits, avoidance of some foods, etc).

An "ad hoc" questionnaire, designed by an expert dietitian, included a list of foods (60 items) most frequently consumed in northen Italy. Commonly consumed portions were specified.

Dietetic interviews were performed by 3 physicians who were trained in assessing habitual food patterns and blinded to the results of the OGTT; other physicians communicated the results of the OGTT to patients after the dietary interviews. The procedures utilized were as follow:

  • photographs were used to compare different portions for each item
  • patients were asked to indicate how often a day and how many days a week they consumed every specific food during the past week
  • data on cooking methods were also collected.

The food list completed by the physicians were entered into a software program (Food Meter, Medimatica s.r.I., Martinsicuro, Teramo, Italy, 1990; modified in 1998 in the University of Turin according to food composition tables by the Italian National Institute of Nutrition). Subgroups of foods within the same category and with similar composition were collapsed in single items. Every item carried the weighted mean of macronutrients or minerals and vitamins. The database contained all foods consumed by the subjects.

  

Description of Actual Data Sample:

Initial N:A total of 26 women with GDM and 84 women with abnormal value of OGTT were identified. During the first month of this period (April 1999-November 2000),all consecutive subjects with a normal glucose tolerance results (294 women) were considered as control sibjects

Attrition (final N):  as above

Age: See Table 1

Ethnicity: Caucasian

Other relevant demographics:

Anthropometrics: see Table 1

Location: University of Torino, Torino, Italy

 

Summary of Results:

Patients with IGT and GDM were older and had significantly higher prepregnancy weights and BMI, short stature and a more frequent history of diabetes in first degre relatives(Table I ).

Table 1: Clinical characteristics of the patients studied

  Normoglycaemia

IGT

GDM

p

Patients (n)

294

84

126

 
Age (years)

31.8±4.4

33.0±4.9

33.0±4.8

0.02

Weight (kg)

62.8±13.3

67.9±15.1

66.7±15.4

0.003

Height (m)

1.63±0.07

1.61±0.06

1.62±0.06

0.02

BMI (kg/m2)

23.6±4.6

26.0±5.5

25.4±5.3

0.00002

Nulliparous (%)

62

57

55

NS

Smoking (%)

27

25

33

NS

Familial diabetes (%)a

28

33

41

0.04

Physical activity      

 

Light (%)

21

21

24

NS

Moderate (%)

65

66

67

NS

Vigorous (%)

14

13

9

NS

Fasting insulin (pmol/l)

72.0±75.6

130.2±187.2

116.4±186.0

0.0081b

 a First-degree relative

b After adjustment for BMI

The women with IGT and GDM,considered as a single group displayed a significantly higher percentage of fat intake (as % of total kcal)than the control subjects, p=0.03). IGT and GDM patients ate significantly higher percentage of saturated fat (% total fat). This difference was still significant, when saturated fat was expressed as percentage of total kilocalories (Table 2).

 Table 2:Nutritional data obtained by dietary assessment

  Normoglycemia IGT GDM p
Alcohol (gr/day) 2.98±7.4 1.78±6.7 3.78±7.7 NS
Total energy (cal) 2035±627 2002±568 1889±490 NS
Fat (% kcal) 31.8±7.6 33.1±7.4 33.6±9.1 NS
Protein (% kcal) 14.8±2.5 14.9±2.9 14.3±2.4 NS
Carbohydrate (% kcal) 52.6±7.7 51.6±8.2 51.2±9.0 NS
Complex carbohydrate(% total carbohydrate) 58.8±11.1 59.0±13.5 57.3±12.8 NS
Fat (% total fat)        
Saturated 34.4±6.7 35.8±8.3 36.5±11.0 0.04
Polyunsaturated 21.8±5.0 21.3±3.7 20.7±4.7 NS
Monunsaturated 43.8±3.8 42.8±5.9 42.8±7.1 NS
Fat (% total kcal)        
Saturated 10.9±3.1 11.7±3.1 12.0±4.4 0.004
Polyunsaturated 6.9±2.2 7.1±2.1 7.0±2.7 NS
Monousaturated 14.0±3.9 14.3±4.2 14.5±4.9 NS
P:S ratio 0.70±0.51 0.64±0.22 0.63±0.25 NS
Fiber (gr) 16.4±5.3 16.3±4.6 15.2±4.9 NS

In a multiple logistic regression model, age, lower height, familiar diabetes BMI and percentage of saturated fat (percentage of total fat) were all associated with the presence of IGT/GDM after adjustment for gestational age (Table 3).

Table 3: Multiple logistic regression analyses evaluating the association of IGT/GDM with the variables listed in all patients and in those without first degree first-degree diabetic relatives,not overweight and younger than 35 years of age (right column).

Independent variables

All patients(n=504) Without risk factors(n=173)
 

 OR;95%-CI;p

 OR;95%-CI;p

Age

1.3a,1.1-1.16;0.008

0.8a;0.5-1.3;NS

Height

 0.7;0.5-0.9;0.03b

 0.6;0.3-1.1;NSb

Familial diabetes c

 1.5;1.1-2.3;0.03

 1.5;0.7-3.2;NS

Class of BMId

 1.8;1.3-2.3;0.00002

 
Saturated fat (%of total fat)

 1.3e;1.1-1.6;0.02

 2.0e;1.2-3.2;0.007

Polyunsaturated fat (%total fat)

 0.96;0.92-1.00;NS

 0.85;0.77-0.92;0.003

aFor each five years of age increase

bFor each 10cm increase

c Diabetes in any relative

d Normal weight (BMI<25 kg/m2); overweight (BMI>=25 and <30kg/m2); obesity (BMI>30 kg/m2).

e For 10% increase of saturated fat

Other Findings

The 40 women IGT/GDM without risk factors showed a lower P:S ratio, when compared to the 133 normoglycaemic patients (respectively 0.49±0.17 vs 0.73±0.72; p=0.04).

Author Conclusion:

* Saturated fat has an independent role in the development of gestational glucose abnormalities. A higher intake of polyunsaturated fat appeared to be protective.

* This above noted role is more important in the absence of conventional risk factors suggesting that glucose abnormalities could be prevented during pregnancy, at least in some groups of women

Reliability: 

Total energy (kcal/d) - the reliability of the reported energy intake was assessed by calculating the ratio of estimated energy intake on predicted basal metabolic rates using age-and sex-specific formulas derived by Schofield et al. A value of 0.88 which represented the 97.55 confidence interval (CI), was the cut-off point for under-reporting. The 18 under-reporters (3.6%), according to the above formula, were equally distributed across the three categories of glucose tolerance.  

Analytical quality of serum levels of selenium and zinc was checked by analyzing standard reference materials (normal human serum) at two concentration levels (UTAK B1, level trace elements: normal-range code 66816 and high range code 66815). Results showed that analytical procedures were reliable.

  • Limitation:

    Dietary interviews-self reported but because most of these women were cooking for their families, considered to be the best source of information.

  • Funding Source:
    University/Hospital: University of Turin, S. Giovanni Battista Hospital
    Reviewer Comments:

    The limitations 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) ???
     
    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.) Yes
      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? Yes
      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.) 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? 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? ???
      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)? N/A
      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? 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