GDM: Abnormal Glucose Tolerance During Pregnancy (2008)
To examine maternal characteristics and delivery complications in relation to the outcome of a 75-g, 2-hour glucose tolerance test at 25 to 30 weeks' gestation.
The analysis was restricted to singleton pregnancies and was made on material of singleton deliveries in Lund University Hospital for which data from the computerized register of deliveries could be matched from the Medical Birth Registry.
The exclusion criteria was not delineated.
Recruitment: The study was restricted to deliveries occurring in 4 hospitals located in the study area.
Design : Cohort study
Blinding used (if applicable): not applicable
Intervention : In the clinical care of the pregnant woman, the control and the sub-GDM groups were treated in the same way, without an consideration of the glucose level.
- All women with identified GDM were treated at the center for antenatal care in Lund University Hospital.
- All were given a device for home blood glucose monitoring
- Blood glucose was tested 6 times daily if the woman was insulin treated and 6 times every other day if not.
- All women with GDM had telephone contact with a diabetalogist every week or every second week. Approxmately 40% of the women were treated with insulin.
Statistical Analysis
- Statistical analysis was performed with the Mantel-Haenszel method after various stratifications.
- Each group was compared with all other groups
- The 95% confidence intervals were determined by a t-test–based method.
Timing of Measurements
- Pregnant women were offered an oral GTT, which was recommended to be done at week 27 or 28 weeks of pregnancy.
- The tests were performed in the morning after overnight fasting.
- Anhydrous 75 g glucose dissolved in 300 mL. of water was given.
- After 2 hours , a sample for determination of a 5 µL capillary whole-blood glucose value was collected in a microcuvet and immediately analyzed for glucose level in a Hemocue (Hemocue AB, Ângelholm, Sweden) apparatus.
Dependent Variables
- Maternal age
- Parity
- Smoking was used as a proxy of socioeconomic status
- Mode of delivery: noninstrumental, forceps or vacuum extraction, elective cesarean, emergency cesarean, unknown
Independent Variables
Blood glucose values:
- Sub-GDM Group- mean 2-hr glucose level: > 7.8 mmol/L(140-162 mg/dL). The cut-point value of 7.8 has been recommended by the World Health Organization.
- Control group: mean 2-hr glucose level=< 7.8 mmol/L(<140 mg/dL)
- To these 2 groups were added women with manifested GDM( defined as a glucose value of > 9 mmol/L [ >162 mg/dL]). These women were identified either during the screening procedure or as a result of testing performed outside the defined weeks because of clinical signs ,heredity, or previous GDM.
- Gestational Diabetes-the definition of GDM – a 2-hour value of at least 9 mmol/L( > 162 mg/dL) after a 75-g oral GTT. Whole venous glucose values are 1.1 mmol/L lower than whole-blood capillary values and are similar to plasma venous values
- Maternal weight at delivery
- Gestational duration
- Infant's birth weight
- Umbilical artery pH
- Apgar score
- Placental weight
Control Variables
Initial N: 4528 postpartum women (antenatal care).
Attrition (final N): A total of 144 women with GDM were identified.
Age: < 19 years- > 45years of age
Ethnicity:
Other relevant demographics:
Anthropometrics
Location: Department of Obstetrics and Gynecology and the Department of Internal Medicine/Diabetes, Lund University Hospital and the Department of Obstetrics and Gynecology, Helsingberg Central Hospital.
Participation was decreased among teenagers, the highest participation was by women between 20 and 29 years of age. No significant effect of parity or maternal smoking was seen (Table I ).
Table 1. Odds ratio to participate in oral GTT screening according to various maternal characteristics-Maternal age, parity, and smoking
|
Characteristic |
Odds ratio |
99% Confidence interval |
|
Maternal age |
_ |
_ |
|
<19 y |
0.73 |
0.58-0.91 |
|
20-24 y |
1.14 |
1.04-1.24 |
|
25-29y |
1.07 |
1.01-1.14 |
|
30-34y |
0.91 |
0.86-0.97 |
|
35-39y |
0.93 |
0.84-1.02 |
|
40-49y |
0.97 |
0.77-1.22 |
|
> 45 y |
1.26 |
0.49-3.25 |
|
Parity |
_ |
_ |
|
1 |
0.94 |
0.89-1.00 |
|
2 |
1.06 |
0.99-1.12 |
|
3 |
1.06 |
0.97-1.16 |
|
4 |
0.94 |
0.81-1.10 |
|
> 5 |
0.88 |
0.73-1.07 |
|
Smoking |
1.05 |
0.96-1.14 |
At the analysis of each factor, stratification for the other 2 factors and for the delivery hospital was made (N=14,078).
In Table 2, there was a clear cut trend according to glucose class for maternal age (P<.001 for both glucose classes) but none for parity (P=.39 and P=.25, respectively).
Table II. Odds ratio for having increased glucose level according to maternal age (stratified for parity ) or parity (stratified for age).
| Blood glucose value>>>>>>>>>>>>> | of 7.8-8.9 mmol/L | Gestational> | Diabetes | |
|
(140-162 |
mg/dL) | |||
|
Odds ratio |
95% Confidence interval |
Odds ratio |
95% Confidence interval |
|
| Maternal age |
_ |
_ |
_ |
_ |
| 15-19y |
0.61 |
0.09-4.39 |
- |
- |
| 20-24y |
0.39 |
0.19-0.80 |
0.34 |
0.15-0.77 |
| 25-29y |
0.95 |
0.66-1.37 |
1.16 |
0.79-1.70 |
| 30-34y |
1.09 |
0.76-1.56 |
0.79 |
0.54-1.17 |
| 35-39y |
1.50 |
0.96-2.36 |
1.56 |
0.95-2.56 |
| 40-44y |
1.99 |
0.88-4.50 |
3.13 |
1.57-6.25 |
| 45-49y |
- |
- |
10.87 |
1.79-66.1 |
| Parity |
- |
- |
- |
- |
| 0 |
0.89 |
0.62-1.28 |
0.85 |
0.60-1.25 |
| 1 |
1.29 |
0.90-1.84 |
1.15 |
0.79-1.69 |
| 2 |
0.63 |
0.37-1.17 |
1.03 |
0.67-1.68 |
| 3 |
1.08 |
0.46-2.55 |
- |
- |
| > 4 |
1.35 |
0.50-3.62 |
- |
- |
Reference values are for women with a glucose value of <7.8 mmol/L (<140 mg/dL). Each maternal age or parity group is compared with all other age or parity groups.
In the sub-GDM group , the total cesarean delivery rate was 13.8%, versus 7.7% in the control group. An odds ratio comparing elective cesarean delivery in the sub-GDM group and in the control group with all other delivery methods , stratified by year of birth, maternal age , and parity, was 1.77(95% Confidence Interval, 1.01-2.86). For emergency cesarean delivery the corresponding odds ratio was 1.69 (95% confidence interval, 1.01-2.86)(Table III).
Table III. Mode of delivery (at Lund University Hospital) of singleton pregnancies according to blood glucose level
|
Blood-- |
glucose-- |
level-- |
||||
|
---- |
<7.8 mmol/L |
(<140mg/dL) |
7.8-8.9 mmol/L |
(140-162 mg/dL) |
Gestational |
diabetes |
| Mode of delivery |
No. |
% |
No. |
% |
No. |
% |
| Noninstrumental |
3985 |
86.3 |
104 |
79.4 |
85 |
73.3 |
| Forceps or vacum extraction |
251 |
5.4 |
7 |
5.3 |
7 |
6.0 |
| Elective cesarean |
108 |
2.3 |
6 |
4.6 |
8 |
6.9 |
| Emergency caesarean |
249 |
5.4 |
12 |
9.2 |
13 |
11.2 |
| Unknown |
23 |
0.5 |
2 |
1.5 |
3 |
2.6 |
| Total |
4526 |
- |
131 |
- |
116 |
- |
Other Findings
- The maternal BMI was lower in the group with the lowest glucose level than in the groups with higher levels, which seems to be partly a result of greater body weight but also of shorter height.
- The ratio between infant and maternal initial weights (at first antenatal visit ) increased slightly in the sub-GDM group but decreased in the GDM groups.
- The ratio of infant weight over placental weight decreased with increasing glucose values.
- The study stressed the significance of moderately increased oral glucose tolerance values.
- In the gestational diabetes group, advanced maternal age and high body mass index were risk factors for increased oral glucose tolerance values in 12,657 screened women.
- Those women with 2-hour oral GTT values of 7.8 to 8.9 mmol/L had an increased risk of having a nonoptimal delivery outcome.
Limitations were noted related to the "smoking" variable
-
After stratification for smoking the difference in birthweight increased. One explanation culd be that smoking increases insulin resistance. On the other hand, women with gestational diabetes smoked significantly less than the control group. The researchers noted that is was difficult to explain the decreased frequency of smoking in women with GDM.
Inclusion/exclusion criteria not well defined.
The limitations and critique of the study, as stated by the authors appear to be very appropriate.
Analytical longitudinal surveys refer to what epidemiologists term prospective or cohort studies. A Cohort Study is a study in which patients who presently have a certain condition and/or receive a particular treatment are followed over time and compared with another group who are not affected by the condition under investigation. Studies of this kind provide a better opportunity than one time cross sectional studies to examine whether certain behaviors do in fact lead to (or cause) the disease.
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Quality Criteria Checklist: Primary Research
|
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| 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? | ??? | |
| 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? | Yes | |
| 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? | 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? | Yes | |
| 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? | Yes | |
| 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? | 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)? | Yes | |
| 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? | Yes | |
| 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 | |