GDM: Weight Management (2008)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
  • To investigate the differences in prepregancy weight status and the pattern of weight gain between women who deliver term vs preterm
  • To test the hypothesis that inadequate weight gain in the third trimester, based on a definition that was prepregancy weight status specific, is predictive of a preterm birth
  • To determine whether the effect of prepregnancy weight status and inadequate weight gain differed according to the etiological pathways of a preterm birth
Inclusion Criteria:
  • Primigravida
Exclusion Criteria:
  • Induced labor
  • Still birth
  • Multiple birth
  • Missing data
Description of Study Protocol:

Recruitment

Data collected prospectively from 9651 pregnant women receiving prenatal care in the public health clinics in the West Los Angeles area from 1983 to 1987.

Design:  Cohort Study

Blinding Used (if applicable):  not applicable

Intervention (if applicable):

  • Demographic information collected on all women.
  • Prepregnancy weight, and weight gain and maternal hematocrit.
  • Classification of inadequate weight gain by prepregnancy weight status if weight gain was less than:  0.34 kg/wk, underweight; 0.35 kg/wk, normal weight, 0.30 kg/wk, overweight and obese women

Statistical Analysis

Student's t test for continuous variables and chi-square statistics for categorical variables were used to determine significant differences between mothers who delivered term and preterm.  Mantel Extension was used to test whether the odds in successive BMI groups associated with preterm births increased or decreased when compared with a baseline group.  Multivariate logistic regression was used to isolate the role of prepregnant weight status and adequacy of weight gain from other factors that may influence birth outcome.

Data Collection Summary:

Timing of Measurements

Data collected prospectively and examined.

Dependent Variables:

  • Length of gestation
  • Preterm labor <37 wk
  • Premature rupture of membranes (PROM) as a delivery <37 wk with spontaneous rupture of the amniotic membranes before the onset of labor
  • Term birth: delivery >37 wk gestation

Independent Variables

  • Prepregnancy weight status

Control Variables

Description of Actual Data Sample:

Initial N:  Complete data on 7589 women.

Attrition (final N):  7589 women

Age:  18-34 yr (91%)

Ethnicity:  predominantly Hispanic (80%)

Other relevant demographics:  Married (61%), in prime childbearing age,  and of low educational level (52%, < 8 yr), 50% entered prenatal care between 10 and 20 wk gestation.

Anthropometry:

Location:  West Los Angeles, California

 

Summary of Results:

Other Findings

The prevalence of preterm births and intrauterine growth retardation was 6.6 and 6.0% respectively.

Women who delivered preterm were significantly lower in prepregnancy weight and as a result had a lower mean prepregnant BMI than women who delivered term.

In addition, mothers of preterm infants were less frequently married, more likely to smoke, to be African-Americans and had more occurrences of uterine bleeding and blood pressure abnormalities (chronic hypertension and/or pregnancy induced hypertension) than mothers of term infants.

Multivariate logistic regression techniques were used to isolate the role of each nutritional variable from other factors that may influence birth outcomes. 

Women who delivered preterm had patterns of weight gain similar to women delivering term infants.

Underweight status (BMI >19.8 kg/m2) before pregnancy nearly doubled the likelihood of delivering preterm 1.98( 95% CI, 1.33-2.98).  There was a significant trend of increasing risk for preterm births associated with decreasing BMI ( P<0.001)

Inadequate weight gain in the third trimester increased the risk of delivering preterm: 1.91 ( 95% CI, 1.40-2.61)

An inadequate weight gain in the third trimester increased the risk of preterm labor by 75% and more than doubled the risk of premature rupture of amniotic membranes.

Author Conclusion:

Preconceptional nutrition counseling and promotion of adequate weight gain during the third trimester of pregnancy should be components of public health programs designed to decrease the prevalence of preterm births.

Our study demonstrated that a high risk woman’s chance of delivering preterm could be cut substantially with normal weight status before pregnancy and adequate gestational weight gain. In addition, a 17% reduction in the risk of preterm birth would occur in this predominantly Hispanic population if inadequate weight gain alone was resolved.

Considering the fact that prematurity is a major contributor to infant mortality, such reductions in preterm birth could have a significant public health impact on the infant mortality rate.

Since the majority of the subjects were low income Hispanic women the results may not generalize to other women.

Funding Source:
Government: State of California Maternal and Child Health Branch
University/Hospital: University of North Carolina, Cedars-Sinai Medical Center
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:

Weight gain in the third trimester should be monitored more closely during pregnancy to prevent preterm deliveries.

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) N/A
  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) N/A
 
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? ???
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) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  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? 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? 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? Yes
  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? Yes
  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? Yes
  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)? 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? 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