Reviewer's report
Title:A Multicentre Matched Case Control Study of Risk Factors for
Preeclampsia in Nulliparous and Parous Women in Pakistan
Version: 1Date:11 November 2009
Reviewer: Chunfang Qiu
Reviewer's report:
Major Compulsory Revisions
Title
The title mentioned the parity; however, the reader did not get any information of
it from this paper.
Methods
1 Matched for parity: A matched case-control study can be used to control for the
effects of potential confounding variables in the study design. The major
advantages of matching are that it may be both cost-effective and efficient under
the right set of circumstances. Another advantage of matching on potential
confounding variables, rather than adjusting for potential confounders during
analysis, is that the functional form for the relationship between the confounding
variable and the outcome need not be specified, and thus matching provides a
superior method to control confounding. The match factors in this study included
delivery hospital and delivery date as well as parity. Nulliparity is a known risk
factor for preeclampsia. If the paper is the first report of such topic in Pakistan
population as the authors claimed, the reader think it’s more appropriate to report
the nulliparity (yes vs. no) and report the related unadjusted / adjusted OR rather
than matching for parity and lost the chance to explore this important factor.
2 Definition of controls: the exclusion is”who did not have a diagnosisi of
pre-eclampsia”, the reader wonder if pre-pregnancy hypertension or proteinuria
patients were included in the control group.
3 Page 5, “body mass index”-------Please specify if it is pre-pregnancy BMI. And
how the author obtained the information. (In P10 in Discussion section, it is
stated that “prepregnancy weights and body mass index were assessed by
substracting the average weight gain from the full term maternal weight
which------”.)
4 Sample size calculation in page 5-6 seems irrelevant to this paper (it relates to
diabetes instead of preeclampsia).
5 P6 indicated the procedure of how to select the final multivariate logistic
regression model. Do the authors consider the possible collinearity between
family history of DM, history of DM and GDM in the same model if putting all
these variables in the same model?
Results
1. What is the gestational age of delivery in PE case or control subjects? What is
the gestational age of PE diagnosis? Report them also in Table I.
2. The statement “No significant differences were observed between cases and
controls with regards to maternal socioeconomic status such as-------” did not
match the results of monthly household income in Table I. What’s the unadjusted
and adjusted OR of preeclampsia for household income?
3. in P5, the authors listed the potential variables such as “------maternal
smoking, age at menarche, past history of PE, blood group and RH factor”, how
about show it in the Table I and explain the results in text?
4. P6 indicated the procedure of how to select the final multivariate logistic
regression model. How about list the variables included in the final model in the
text, and in the footnote of table II?
Discussion
1. Limitation: the author used Perceived Stress Scale (PSS) to evaluate the
stress level in the past month. However, due to its case-control study design, the
PSS score was collected postpartum which could result in the recall bias. Also if
the preeclampsia was diagnosed in the past month, it could not clarify the
temporal relationship between elevated Perceived Stress Scale score and
increased preeclampsia risk.
2. The estimates of “preexisting diabetes mellitus------There were few control
subjects (n=2) with a positive history of diabetes when assessing preeclampsia
risk. The confidence interval is even wider when estimating the adjusted OR in
the multivariate logistic regression model.
Table I
1. Please report the distribution of parity, maternal smoking, age at menarche,
past history of PE, blood group and RH factor etc.
2. Please clarify the weight, BMI as pre-pregnancy.
Table II
How about list the variables included in the final model in the footnote of table II?
Minor Essential Revisions
1. The term of “potential confounding variable” used in page 5 is not appropriate.
They are the interesting variables explored in this risk factor paper.
2. Please report the detailed categories of the continuous variable such as
maternal age (<20. 25-34, #35), BMI (lean<18.5, normal 18.5-24.9, overweight
25-29.9 and obesity #30 kg/m2) as well as paternal age (<20. 25-34, #35) etc.
3. Table 1, please format the presentation of some variable such as family history
of hypertension etc.
Level of interest: An article of limited interest
Quality of written English: Acceptable
Statistical review: Yes, and I have assessed the statistics in my report.
Declaration of competing interests:
I declare that I have no competing interests.