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Jeanet M Kemmeren Julius Centre for General Practice and Patient
Oriented Research, University Medical Centre Utrecht, PO Box 85500, 3508 GA Utrecht, Netherlands
Correspondence to:
A Algra A.Algra{at}neuro.azu.nl
Objective:
To evaluate quantitatively articles that
compared effects of second and third generation oral contraceptives on risk of venous thrombosis.
What is already known on this topic
What this study adds
Design:
Meta-analysis.
Studies:
Cohort and case-control studies assessing risk of venous thromboembolism among women using oral contraceptives before October 1995.
Main outcome measures:
Pooled adjusted odds ratios
calculated by a general variance based random effects method. When
possible, two by two tables were extracted and combined by the
Mantel-Haenszel method.
Results:
The overall adjusted odds ratio for third versus second generation oral contraceptives was 1.7 (95% confidence interval 1.4 to 2.0; seven studies). Similar risks were found when oral
contraceptives containing desogestrel or gestodene were compared with
those containing levonorgestrel. Among first time users, the odds ratio
for third versus second generation preparations was 3.1 (2.0 to 4.6;
four studies). The odds ratio was 2.5 (1.6 to 4.1; five studies) for
short term users compared with 2.0 (1.4 to 2.7; five studies) for
longer term users. The odds ratio was 1.3 (1.0 to 1.7) in studies
funded by the pharmaceutical industry and 2.3 (1.7 to 3.2) in other
studies. Differences in age and certainty of diagnosis of venous
thrombosis did not affect the results.
Conclusions:
This meta-analysis supports the view that third generation oral contraceptives are associated with an increased risk of venous thrombosis compared with second generation oral contraceptives. The increase cannot be explained by several potential biases.
Third generation oral contraceptives have been reported to increase the
risk of venous thrombosis compared with second generation oral
contraceptives
Women taking third generation oral contraceptives have a 1.7-fold
increased risk of venous thrombosis compared with those taking second
generation oral contraceptives
© BMJ 2001
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