Gestational Weight Gain and Postpartum Diabetes

Association between Gestational Weight Gain and Postpartum Diabetes: Evidence from
a Community Based Large Cohort Study
Q1. Did the study address a clearly focused issue?
Answer: Yes, the study has clearly focused on the issue – the association between GWG and
diabetes in later life which has possible biological plausibility because of the link between
GWG, PPWR and the development of obesity. Mater-University of Queensland Study of
Pregnancy (MUSP) cohort study has available prospectively collected data of women on
GWG during pregnancy and self reported diabetes 21 years post-partum. This provides a
unique opportunity to examine the association of GWG with diabetes in later life.
Q2. Was the cohort recruited in an acceptable way?
Answer: Yes, the participants of the cohort was recruited in an acceptable way. Written
informed consent from the mothers was obtained at all data collection phases of the study.
Ethics committees at the Mater Hospital and the University of Queensland approved each
phase of the study. In this study 7223 mother-child pairs were prospectively followed with
assessments when their offspring were 6 months, 5, 14 and 21 years. The present analyses are
limited to a sub-sample of 3386 mothers for whom complete data was available on weight
gain during pregnancy, pre-pregnancy BMI and self-reported diabetes 21 years post-partum.
Q3. Was the exposure accurately measured to minimise bias?
Answer: Yes, exposure GWG is accurately measured in the study. Maternal pre-pregnancy
weight was self-reported recorded at baseline from maternal questionnaires. Last weight was
measured at 39 weeks gestation when mothers gained maximum weight and this information
was abstracted from the medical chart by an obstetrician associated with the MUSP. Using
these two measures (first and last weight) of weight, total weight gain during pregnancy was
defined. Then, total GWG was classified into inadequate, adequate, or excess weight
according to IOM guidelines. This was the main exposure of the study.
Q4. Was the outcome accurately measured to minimise bias?
Answer: No, the outcome of this study was self-reported diabetes mellitus at 21 years postpartum. This information was gathered using a self-administered questionnaire and it might
cause bias.
Q5. a) Have the authors identified all important confounding factors?
Answer: Yes, the study had included potential confounding factors. Available potential
confounders were maternal pre-pregnancy BMI, maternal age at FCV (in years), maternal
educational levels, parental ethnic origins, maternal pregnancy consumption of cigarettes, TV
watching and exercise.
Q5. b) Have they taken account of the confounding factors in the design and/or analysis?
Answer: Yes, the confounding factors were taken into analysis. To examine, logistic
regression was used to estimate the OR of experiencing diabetes by 21 years post-partum. A
series of logistic regression models to estimate the odds of being diabetic with adjustment of
potential confounding factors. All the multivariable analyses were conducted for the multiple
imputation data to increase the statistical precision
Q6. a) Was the follow up of subjects complete enough?
Answer: Yes, the follow-up of the subjects is complete enough as the sub-sample of 3386
women were available in the cohort to establish the link between GWG with diabetes 21
years after pregnancy. However, missing items were managed using a multiple imputation
method that impute missing data from the sub-sample of 3386 women to increase the
statistical precision.
Q6. b) Was the follow up of subjects long enough?
Answer: Yes, follow-up of the subjects was long enough more than two decades from index
pregnancy. Mothers were prospectively followed with assessments when their offspring were
6 months, 5, 14 and 21 years.
Q7. What are the results of this study?
Answer: At 21 years post-partum, 8.40% of mothers self-reported a diagnosis of diabetes
made by their doctor. In the age adjusted model, we found mothers who gained excess weight
during pregnancy were 1.47(1.11,1.94) times more likely to experience diabetes at 21 years
post-partum compared to the mothers who gained adequate weight. This association was not
explained by the potential confounders including maternal age, parity, education, race,
smoking, TV watching and exercise. However, this association was mediated by the current
BMI. There was no association for the women who had normal BMI before pregnancy and
gained excess weight during pregnancy. The findings of this study suggest that women who
gain excess weight during pregnancy are at greater risk of being diagnosed with diabetes in
later life.
Q8. How precise are the results?
Answer: The result of the study is precise as the estimated effect size of the adjusted model
found with more robust confidence interval (OR: 1.47, CI 1.11, 1.94). However, relatively
large sample size of the study assists to derive a more precise estimate with narrow CI.
Q9. Do you believe the results?
Answer: Yes, the result of the study is believable as the study is methodologically strong
including sample selection, in measurements of exposure, outcome and several confounders
and mediators and used more robust statistical analysis that efficiently manage missing data.
However, the result of the study supports existing evidence in terms of strength and direction.
This study also adds with existing evidence by establishing long term link between GWG and
diabetes.
Q10. Can the results be applied to the local population?
Answer: No, the result of the study is not applicable to the local population. The MUSP
sample comprises effectively all consecutive births of public patients over 3 years, ensuring a
broad cross section of mid to lower socio-economic status births. Participants were not
selected on the basis of any physical or social characteristic. Thus MUSP is not representative
of all Australian families.
Q11. Do the results of this study fit with other available evidence?
Answer: Yes, finding is consistent with existing evidence showing that excess GWG predict
post-partum weight retention and higher BMI in the short and long term which contributes to
metabolic dysfunction and diabetes.
Q12. What are the implications of this study for practice?
Answer: Yes, this study adds weight to the argument that excessive weight gain during
pregnancy, particularly for overweight women is not only important in the short term but has
long term health implications.