Evidence Table 9Patient Risk Factors – oral contraceptives

Bibliographic referenceStudy TypeEvidence levelNo. of patientsPatients characteristicsExposureLength of follow up/exposureOutcome measuresEffect sizeComments
Edmonds et al., 2004169Systematic review with 2 case control studies and 5 cohort studies2+Not stated for all studiesPatients undergoing general, elective gynaecological, emergency gynaecological, thoracic, orthopaedic, neurological or urologic surgery.

Other inclusion criteria:
1 study - adults
1 study – 15–44 yrs
2 studies – /16–40 yrs olds
1 study – 40–80 yrs
3 studies – no other specific patient group
Oral contraceptives

Non-users of oral contraceptives
3 days to 3 months or entire postoperative hospitalisationRisk estimate for postoperative DVTOdds ratio: 2.48
CI: 1.53 to 4.02 (3 studies)
A pooled risk estimate was only possible for three of the studies due to deficiencies in reported data.

Diagnosis of DVT:
3 studies fibrinogen uptake test
1 study Doppler ultrasound and clinical diagnosis
2 studies used discharge data for diagnosis of DVT
1 study not specified
Kemmeren et al., 2001336Systematic review

3 cohort studies
9 case- control studies
3 nested case- control studies
2+1598 cases
3265 controls
Current oral contraceptive users. Data collected from Western countries.3rd generation oral contraceptives:

2nd generation oral contraceptives levonorgestrel
Not reportedRisk estimate for venous thrombosis 3rd vs 2nd generation contraceptivesUnadjusted odds ratio:
1.6 (CI: 1.3 to 1.9)
(4 studies)
Adjusted odds ratio:
1.7 (CI: 1.4 to 2.0)
(3 studies)
Author reports: some studies reported only frequencies, some only unadjusted or adjusted odds ratios. They performed an overall analysis based on the adjusted odds ratios and on the 2x2 tables separately.

*Diagnosis confirmed by ultrasound, plethysmography or venography.

Not all studies in used an objective test to diagnose venous thrombosis.
Risk estimate for venous thrombosis desogestrel vs levonorgestrelUnadjusted odds ratio:
1.9 (CI: 1.5 to 2.3)
(6 studies)
Adjusted odds ratio:
1.7 (CI: 1.2 to 2.6)
(4 studies)
Risk estimate for venous thrombosis gestodene vs levonorgestrelUnadjusted odds ratio:
1.7 (CI: 1.3 to 2.2)
(5 studies)
Adjusted odds ratio:
1.5 (CI: 1.3 to 2.2)
(3 studies)
Risk estimate for venous thrombosis 3rd vs 2nd generation (type of progestagen unspecified)lUnadjusted odds ratio:
1.5 (CI: 1.2 to 1.8)
(4 studies)
Adjusted odds ratio:
1.4 (CI: 1.1 to 1.9)
(3 studies)
Rocha et al., 2007556Systematic review

2 system atic review s

5 case control studies

1 study unclear
2+UnclearUnclearOral contraceptivesUnclearSee comments sectionSee comments sectionResults not reported as all studies except 1 were included in Kemmeren et al., 2001336.

The only study not reported was a systematic review which reached the same conclusion as Kemmeren et al., 2001336

From: Appendix D, Evidence tables

Cover of Venous Thromboembolism
Venous Thromboembolism: Reducing the Risk of Venous Thromboembolism (Deep Vein Thrombosis and Pulmonary Embolism) in Patients Admitted to Hospital.
NICE Clinical Guidelines, No. 92.
National Clinical Guideline Centre – Acute and Chronic Conditions (UK).
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