EAL

GDM: Prevention of GDM Diagnosis (2008)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To investigate the possible relationship between serum selenium concentration and gestational diabetes.

Inclusion Criteria:

Cases:

nondiabetic
without any reported chronic diseases

Exclusion Criteria:

Exclusion criteria was not delineated for cases.

Description of Study Protocol:

Recruitment - not detailed

Design : Case Control

Blinding used: not applicable

Intervention: not applicable

Statistical Analysis

t test

Data Collection Summary:

Timing of Measurements

Measurements compared between cases and controls.

Dependent Variables

Because the selenium concentrations in human serum are very low, a sensitive analytical technique is needed to measure them. The authors selected hydride generation atomic fluorescence spectrometric method to determine serum selinium. The detect limit of such technique developed in their laboratory was reported as about 0.1 µg/L; the sensitivity was reported as adequate for serum selenium determination.
Serum selenium concentation was determined by applying the hydride generation atomic fluorescence spectrometric method on an XDY-2A atomic flourescence spectrometer made by Bejing Haiguang Instrument Co., China. The determination was carried out by using the instrument condition (high voltage: 300 V; atomic temperature: 900 degrees C; lamp current: 60 mA; carrier gas flow rate : 500 mL/min; shield gas flow rate:1000 mL/min). The reduction of the selenium compounds presented in the samples was carried out by using a solution of 0.7% KBH₄ in 0.2% NAOH).
To validate the selenium concentrations obtained in the trials, reference materials for cattle serum (GBWE90006) and human hair (GBW09101) were used for analysis quality assessment.

Independent Variables

age
IGT
GDM
Pregnancy period

Control Variables

Description of Actual Data Sample:

Initial N: Cases = 234 pregnant women (98 suffered from IGT; 46 subjects from GDM, and 90 subjects were normal pregnant women).

Attrition (final N): as above

Age: 19-46 years

Ethnicity: not mentioned

Other relevant demographics:

Anthropometrics

Location: Shanghai Institute of Nuclear Research, Shanghai People's Republic of China

Summary of Results:

The comparisons between normal pregnant women (NPW) and normal women of fertile age (NW) showed that serum selenium levels were significantly lower in pregnant women (p<0.001). (Table 1)

Table 1 Serum Selenium Concentrations (mg/L) in Different Groups and Statistics Analysis Results

Group		Se(mean±s)
Pregnant Women	NPW(n=90)	0.0741±0.0167	-
-	NPW(n=98)	0.063±0.0132	-
-	GDM(n=46)	0.0635±0.0120	-
Normal women of fertile age	NW(n=17)	0.108±0.0170	-
-	-	-	-
t-Test	IGT/NPW	t	5.03
-	-	P	<0.001
-	GDM/NPW	t	3.84
-	-	P	<0.001
-	IGT/NW	t	12.4
-	-	P	<0.001
-	GDM/NW	t	11.5
-	-	P	<0.001
-	NPW/NW	t	7.65
-	-	P	<0.001

There was a reduction of serum selenium concentration with the progress of pregnancy(Table 2).

Table 2 Serum Selenium Concentrations (mg/L) in two Groups Classified According to the Period of Pregnancy

Group		Se(mean±s)
-	-	NPW	IGT & GDM
First period (from 20 to 33 weeks)	-	0.0785±0.0177(n=40)	0.0660±0.0120(n=57)
Second period (from 33 to 42 weeks)	-	0.0707±0.0152(n=50)	0.0615±0.0131(n=83)
t-Test	-	-	-
(First period/Second period)	t	2.25	2.07
-	P	<0.05	<0.05

Other Findings

Serum selenium levels were significantly lower in pregnant women with IGT(p<0.001) and GDM (p<0.001) than in normal pregnant women.
An inverse correlation between the serum selenium concentration and the gestational period was also observed.

Author Conclusion:

Selenium supplementation during gestation for pregnant women, especially with IGT and GDM, should be considered.
The accuracy and reproducibility of the analytical procedures for selenium determinations were assessed using certified reference materials. The results reported were within the range of mean serum selenium values reported in the literature for normal adult women.

Funding Source:

Government:

Chinese Academy of Science

Reviewer Comments:

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

The reference to the 'accuracy and reproducibility 'of the study does address the caveat relevant to diagnostic studies. Diagnostic studies with deficiencies in specific design features have been shown to be associated with bias.

Inclusion/exclusion criteria and recruitment methods were not well defined/described.

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?		???
	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?	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?	???
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.)	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?		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?		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?	N/A
	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?	No
10.	Is bias due to study's funding or sponsorship unlikely?		???
	10.1.	Were sources of funding and investigators' affiliations described?	???
	10.2.	Was the study free from apparent conflict of interest?	???