EAL

GDM: Prevention of GDM Diagnosis (2008)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

Alpha Case Control Study:

To assess the relationship between perceived exertion during usual prepregnancy recreational physical activity and gestational diabetes.

Omega Prospective Cohort Study:

To examine dietary risk factors for preeclampsia.

Inclusion Criteria:

Alpha Case Control Study:

Cases:

preeclamptic women
English speaking women
patients in labor and delivery wards with a diagnosis of gestational diabetes mellitus
abstracts of medical records to identify women meeting the then-current diagnostic criteria for GDM described by the National Diabetes Data Group.

Controls:

English speaking women who remained normotensive and who did not meet the criteria for gestational diabetes according to their abstracted medical records.

Omega Prospective Cohort Study

Women who initiated prenatal care before 16 weeks gestation at hospital affiliated clinics.

Exclusion Criteria:

Alpha Case Control Study: none noted

Omega Prospective Cohort Study:

< 18 years of age
women who did not speak and read English
women who did not plan to carry pregnancy to term
women who did not plan to deliver at either hospital

Description of Study Protocol:

Recruitment :

Alpha case control study- English speaking women with patients in labor and delivery wards with a diagnosis of gestational diabetes mellitus were recruited.

Omega Prospective Cohort Study-Emphasis was on the recruitment of nulliparous women, although multiparous women who were enrolled when study personnel were available.

Design : Alpha study = case control; Omega Study = prospective cohort study

Blinding used: not applicable

Intervention: not applicable

Statistical Analysis : logistic regression models to derive odds ratios (ORs)and 95% confidence intervals(CIs).

Data Collection Summary:

Timing of Measurements

Alpha case control study

Women were routinely screened for GDM between 24 and 28 weeks gestation using a 50-g 1-h oral glucose tolerance test

Omega Prospective Cohort Study

Data collection occurred at or soon after enrollment (13.2 weeks gestation, on average)
Diagnosis of gestational diabetes was made after medical records abstraction of glucose tolerance test results

Dependent Variables

Alpha case control study

Body mass Index - self reported height and weight 3 months before pregnancy were used to calculate body mass index (BMI; weight[kg]/height[m²]).
Dietary variables - a food frequency questionnaire was used to measure dietary intake during the 3 months before pregnancy as well as during pregnancy. The food frequency questionnaire has been validated in nonpregnant populations, but not in pregnant women.
Recreational activity - during interviews, women were asked questions regarding type, frequency, and duration of recreational activities in the year before pregnancy. The questions were derived from the Stanford Seven-Day Physical Activity Recall and the Minnesota Leisure-Time Physical Activity Questionnaire, which has been validated among men and nonpregnant women.

Omega Prospective Cohort Study

Usual perceived activity during recreational physical activity (Borg rating) - Trained interviewers administered a questionnaire nearly identical to that used in the Alpha Study and provided the same food frequency questionaire
Energy expenditure during physical activity (MET-hours/wk) - as a result of small numbers, the energy expenditure categories were combined resulting in categories of 0, 0.1 to 14.9, and >=15.0 MET-hours/week. Again due to small numbers, perceived exertion was categorized as none to moderate (score 0-4), strenuous (5 or 6), and very strenous to maximal (7 to 10).

Independent Variables

Alpha case control study:

Maternal age (years)
Maternal race/ethnicity
Nulliparous
Maternal prepregnancy body mass index (BMI, kg/m²)
<= 12 years education
Unmarried
Periconception dietary fruits and vegetables (servings/d <5)
Smoking during pregnancy
Prepregnancy chronic hypertension
Familial history of chronic hypertension
Familial history of type 2 diabetes
Maternal birthweight (g)

Omega Prospective Cohort Study

Maternal age (yrs)
Maternal race/ethnicity
Nulliparous
Maternal prepregnancy body mass index (BMI, kg/m²)
<= 12 years education
Unmarried
Periconception dietary fruits and vegetables (servings/d <5)
Smoking during pregnancy
Prepregnancy chronic hypertension
Familial history of chronic hypertension
Familial history of type 2 diabetes
Maternal birthweight (g)

Control Variables

Description of Actual Data Sample:

Initial N:

Alpha study=216 cases, 472 controls;

Omega Study=897 participants in prospective cohort study

Attrition (final N): as above

Age: See Table 1

Ethnicity: See Table 1

Other relevant demographics:

Anthropometrics

Location: Center for Perinatal Studies, Swedish Medical Center, Seattle, Washington

Summary of Results:

ALPHA Case STUDY:

There were differences found according to case status for several of the distributions, including age, race, nulliparity, and body mass index, among others (See Table I).

Table 1. Distributions of Gestational Diabetes Mellitus Cases and Control Subjects According to Selected Characteristics, Alpha Study, Washington State, 1998-2002

	Cases	Controls
	(n=216)	(n=472)
Characteristics	%	%
Maternal age (years)	-	-
<20	<1	5
21-34	62	66
35-39	27	24
>= 40	11	5
Maternal race/ethnicity	-	-
White	62	72
Black	10	6
Asian	14	10
Other	13	11
Missing	1	<1
Nulliparous	44	53
Maternal prepregnancy body mass index (BMI, kg/m²)	-	-
<20.0	6	21
20.0-24.9	30	57
25.0-29.9	27	14
>=30.0	36	7
Missing	1	1
<=12 yr of education	19	17
Unmarried	18	20
Periconceptional dietary fruits and vegetables (serving/d)	_	_
<5	61	54
Missing	5	7
Smoking during pregnancy	17	11
Prepregnancy chronic hypertension	7	<1
Familial history of chronic hypertension	55	44
Familial history of type 2 diabetes	31	13
Maternal birthweight(g)	-	-
<2500	12	6
2501-3999	73	80
>=4000	3	7
Missing	12	7

Perceived exertion was inversely associated with risk of gestational diabetes after adjustment for maternal age, race/ethnicity, prepregnancy hypertension, and nulliparity(Table 2).

Table 2. Distributions of Cases and Controls Adjusted * Odds Ratios anf 95% Confidence Intervals for Gestational Diabetes Mellitus According to Measures of Recreational Physical Activity in the Year Before Pregnancy; Alpha Study, Washington State,1998-2002.

	No. Cases	No. Controls	OR
Measure of Activity	(n=211)	(N=267)	(95% CI)
Usual perceived exertion	-	-	-
during recreational physical	-	-	-
activity(Borg rating)	-	-	-
0-2¶	55	35	1.0
3-4	42	63	0.41(0.21-0.82)
5-6	60	156	0.26(0.14-0.47)
7-10	54	213	0.19 (0.15-0.50)
Energy expenditure	-	-	-
during physical activity	-	-	-
MET-hours/wk)	-	-	-
None¶	77	91	1.00
0.1-14.9	58	119	0.66 (0.39-1.11)
15.0-29.9	38	125	0.59 (0.33-1.03)
>=30.0	38	132	0.49 (0.28-0.87)

* All models are adjusted for age,race/ethnicity, prepregnancy hypertension, nulliparity, and prepregnancy body mass index. Seven women with missing BMI and 3 with missing race/ethnicity, were excluded. ¶ Reference category

The reported results of the examination of the relation between perceived exertion and risk of gestational diabetes according to BMI and energy expenditure did not differ substantially between groups (Table 3).

Table 3. Distributions of Study Participants and Adjusted* Odds ratios and 95% Confidence Intervals for Gestational Diabetes Mellitus According to Usual Perceived Exertion During Recreational Physical Activity in the Year Before Pregnancy, Within Subgroups Defined by Prepregnancy Body Mass Index(BMI) or Energy Expenditure; Alpha Study, Washington State,1998-2002).

Usual Perceived Exertion During Recreational Physical Activity(Borg rating)

	No.case/	0-2	3-4	5-6	7-10
Stratifying Characteristics	Total No.	OR	OR(95%CI)	OR(95%CI)	OR(95%CI)
Prepregnancy BMI(kg/m²⁾	-	-	-	-	-
<25	75/ 444	1.00	0.49 (0.19-1.28)	0.31 (0.13-0.71)	0.29 (0.12-0.65)
>=25	136/ 234	1.00	0.31 (0.18-0.82)	0.23 (0.10-0.57)	0.20 (0.08-0.51)
Energy expenditure during physical activity(MET-	-	-	-	-	-
<10	119/ 286	1.0	0.42 (0.19-0.94)	0.34 (0.16-0.72)	0.29 (0.12-0.68)
>=10	92/ 392	1.0	0.22 (0.02-1.99)	0.12 (0.01-1.02)	0.14 (0.02-1.31)

* adjusted for age, race/ethhnicity, parity, and hypertension history. Model stratified by energy expenditure is also adjusted for BMI. Seven women with missing BMI and 3 women with missing race/ethnicity are excluded. ¶ Reference category

Distribution of selected maternal characteristics according to the usual perceived exertion are presented in Table 4.

Table 4. Characteristics of the Study Cohort (n=897) According to Usual Perceived Exertion* During Recreatuinal Physical Activity in the Year Before Pregnancy; Omega Study, washington State, 1996-2000

Usual Perceived Exertion During Recreational Physical Activity(Borg rating)

Characteristics	0-4	5-6	7-10
Maternal age (yrs)	(n=286)	(n=383)	(n=228)
	%	%	%
<20	1	1	1
21-34	71	74	73
35-39	23	20	24
>=40	5	5	3
Maternal race/ethnicity	-	-	-
White	83	87	83
Black	3	2	3
Asian	7	7	8
Other	7	4	7
Nulliparous	79	90	86
Maternal prepregnancy body mass	-	-	-
index (BMI,kg/m²)	-	-	-
<20.0	20	21	19
20.0-24.9	46	56	64
25.0-29.9	21	14	11
>=30.0	13	8	6
<=12 yr of education	8	2	4
Unmarried	13	12	8
Preconception dietary fruits/	-	-	-
vegetables(svg./d) <5	73	66	63
Missing	5	5	4
Smoking during pregnancy	9	5	5
Prepregnancy chronic	-	-	-
hypertension	5	4	5
Familial history of	-	-	-
chronic hypertension	46	49	49
Familial history of	-	-	-
type 2 diabetes	16	15	12
Maternal birthweight (g)	-	-	-
<2500	6	8	7
2501-3999	76	76	79
>=4000	9	7	7
Missing	10	9	8

Both perceived exertion and energy expenditure was inversely associated with risk of gestational diabetes in the Omega Study (Table 5).

Table 5. Distributions of Study Participants and Adjusted* Odds Ratios and 95% Confidence Intervals for Gestational Daibetes Mellitus According to Measures of Recreational Physical Activity Performed During the Year Before Pregnancy; Omega Study, Washington State,1996-2000.

Measure of Activity	Total No.	No. Cases	OR(95% CI)>>>>>>
Usual perceived exertion during	-	-	-
Recreational Physical Activity (Borg rating)	-	-	-
0-4¶	286	19	1.00
5-6	383	15	0.63 (0.31-1.29)
7-10	228	8	0.57(0.24-1.37)
Energy expenditure during	-	-	-
physical activity(MET-hrs/wk)	-	-	-
None¶	78	10	1.00
0.1-14.9	305	21	0.42(0.18-1.10)
>=15.0	514	11	0.14(0.05-0.38)

*All models are adjusted for age, race/ethnicity, prepregnancy hypertension, nulliparity, and prepregnancy body mass index.

¶Reference category

Other Findings

Author Conclusion:

In contrast to the Alpha Study, the association with energy expenditure was stronger than the perceived exertion association. Adjusted ORs among women reporting strenuous and very strenuous to maximal exertion were 0.63(0.31-1.29) and 0.57(0.24-1.37),respectively,compared with negligible to moderate exertion. Women reporting >=15.0 MET-hours/week experienced an 86% risk reduction(0.14; 0.05-0.38) versus inactive women.
The risk of gestational diabetes is inversely related to the exertion perceived during recreational physical activity in the year before pregnancy.
Perceived exertion was inversely associated with risk of gestational diabetes after adjustment for maternal age, race/ethnicity, prepregnancy hypertension, and nulliparity.

Limitations

The food frequency questionnaire had been validated in nonpregnant populations, but not in pregnant women
The questions were derived from the Stanford Seven-Day Physical Activity Recall and the Minnesota Leisure-Time Physical Activity Questionnaire, which has been validated among men and nonpregnant women
Participants of both studies were more likely to engage in in physical activity than the overall American population.
Authors note low participation rates among controls, suggesting the possibility that case and control groups may not have been representative, and that they may have differed in their ability and willingness to report physical activity characteristics.

Funding Source:

Government:

NIH

Reviewer Comments:

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.

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?	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?	???
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.)	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?		Yes
	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?	Yes
	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?	Yes
	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?	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?	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?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes