wileyonlinelibrary.com/journal/jch J Clin Hypertens. 2018;20:614.
©2018 Wiley Periodicals, Inc.
LETTER TO THE EDITOR
Response to: Association between duration of oral
contraceptive use and risk of hypertension: A meta- analysis:
Methodological and statistical issues
We recently received the letter to the editor in response to our re-
cently published work entitled Association between duration of oral
contraceptive use and risk of hypertension: A meta- analysis
Journal of Clinical Hypertension. We appreciate the comments from
regarding this published paper. However, there
are a few points that need to be addressed. First, of a total 6227
retrieved articles (6222: left box and 5: right box), 2961 were ex-
cluded, which included non- human records (n = 527), non- English or
Chinese records (n = 505), and records of repetition (n = 1929; the
first exclusion box on right side). The remaining 3266 articles were
screened for abstracts. Eight full- text articles were excluded, which
included records about the history of hypertension related to the
trend of oral contraceptive use (n = 3), records about menopausal
hormone therapy (n = 1), records removed for the same study popu-
lation (n = 2), records removed for data for prehypertension and el-
evated blood pressure (n = 2; the third exclusion box on right side).
Thus, the number of articles included in qualitative synthesis and
quantitative synthesis (meta- analysis) was 17.
Second, in the study by Chiu et al,
odds ratios (ORs) and
99% confidence intervals (CIs) were provided. But, what we need
were ORs and 95% CIs, so we didn’t directly use the data that the
original article provided. We calculated the crude ORs and 95%
CIs with 4 table data by STATA version 12.0. The crude ORs (45-
58 years: 1.2, 58- 66 years: 0.9, >67 years: 0.9) were close to the
ORs provided by the original article (45- 58 years: 1.1, 58- 66 years:
0.9, >67 years: 0.9).
In our meta- analyses, we evaluated the highest versus lowest
category of oral contraceptive use and the risk of hypertension. So
we calculated the association between >10 years oral contracep-
tive use and the risk of hypertension in studies by Chiu et al.
for sample size, the number of oral contraceptives user in <58 years
aging group for more than 10 years is 4067, among which the pro-
portion of patients with hypertension is 11%. Accordingly, the
number of never user (<58 years) is 1411, among which the pro-
portion of patients with hypertension is 8.9%. The total number is
5478 (n = 4067 + 1411), and the number of hypertension patients
is 573 (n = 4067 × 11% + 1411 × 8.9%). The other aging groups
(58- 66 years, >67 years) shared the same calculation method.
Third, the basic meanings of RR, OR, and HR are similar, indicat-
ing the relationship between exposure factors and risk of disease. In
general, meta- analysis directly pooled RR, OR, and HR. Similar meta-
analysis statistical methods can also be found in study conducted by
Ettehad et al.
CONFLICT OF INTEREST
Hui Liu MD
Dongfeng Zhang MD
Department of Epidemiology and Health Statistics, The School of Public
Health of Qingdao University, Qingdao, Shandong, China
Dongfeng Zhang, Department of Epidemiology and Health Statistics,
The School of Public Health of Qingdao University, Qingdao, Shandong,
1. Liu H, Yao J, Wang W, et al. Association between duration of oral
contraceptive use and risk of hypertension: a meta- analysis. J Clin
Hypertens (Greenwich). 2017;19:1032-1041.
2. Asgari S. Association between duration of oral contraceptive use and
risk of hypertension: a meta- analysis: methodological and Statistical
Issues. J Clin Hypertens (Greenwich). 2017;19:1032-1041.
3. Chiu CL, Lind JM. Past oral contraceptive use and self- reported
high blood pressure in postmenopausal women. BMC Public Health.
4. Ettehad D, Emdin CA, Kiran A, et al. Blood pressure lowering for pre-
vention of cardiovascular disease and death: a systematic review and
meta- analysis. Lancet. 2016;387:957-967.