Sir,
We read the article by Cho et al.1 with great interest
and would like to appreciate the authors for their novel and interesting
study on the association between postpartum haemorrhage (PPH) and the
occurrence of cardiovascular disease (CVD) beyond the peripartum period.
Moreover, the large number of study subjects derived from a
comprehensive national database was impressive. However, we wish to
point out some issues that may influence the interpretation of their
results. With respect to these issues, we have three suggestions for
this study.
Our first suggestion is regarding the confounding factors. We believe
that there are some important residual and more suitable confounding
factors in the present study. First, the regular use of heparin or
aspirin around the time of delivery can be important residual
confounding factors. This is because they both have risks for
haemorrhage and thromboembolism (e.g. , in cases of
antiphospholipid syndrome, deep venous thrombosis by any underlying
conditions, and high risk of preeclampsia).2,3 Second,
if possible, adjustment for gestational diabetes mellitus, which is
quite common in pregnancy and can be a risk factor for future ischemic
heart disease,4 may be more suitable than
non-gestational diabetes mellitus. Finally, we would recommend adjusting
for HELLP syndrome and acute fatty liver of pregnancy as more suitable
confounding factors than abnormal liver function test, because these are
directly related to bleeding and thrombosis.2 We
believe that adjustment of such residual and more suitable confounding
factors will lead to internally validated results.
Our second suggestion is regarding the external validity of the study.
In this study, more than 60% of the initial population was excluded,
resulting in a substantial reduction in external validity. Although the
authors have conducted a sensitivity analysis including most of the
excluded population, details for this analysis, adjusted confounding
factors, description of missing values, and how the authors dealt with
them were not available. Such insufficient data presentation will make
it difficult for readers to interpret their results regarding external
validity. Hence, clarification of the background of the excluded
population and detailed methods of sensitivity analysis are important.
Our third suggestion is regarding the presentation of the treatment
options for PPH. We can assure the authors that clinicians commonly
consider treatments such as hysterectomy and interventional radiology
(IVR) for PPH.2 These factors could potentially serve
as indicators of severity, because severe PPH may be frequently treated
with these treatments, and the recipients may have a high risk of
developing future CVD. It may be helpful to categorise patients treated
with or without hysterectomy or IVR instead of transfusion.
Once again, we thank the authors for providing such novel and relevant
study findings. However, as discussed above, we believe that this study
may have insufficient internal validity due to the presence of residual
and more preferable confounding factors, as well as reduced external
validity due to the sample size reduction. We believe that addressing
both these issues and a detailed descriptions/analysis regarding
hysterectomy and IVR will make future clinical research more
informative.