The review included 17 case-control studies in total, but only eight of these studies reported data on OC usage (263 women with CVT and 2,862 women without CVT).
Most of the studies were described as high quality. Six of the 8 OC studies used matched case and control participants.
Participants who used OCs showed a significantly increased risk of CVT in comparison with controls who did not use OCs (OR 5.59, 95% CI: 3.95, 7.91, p<0.001). Significant heterogeneity was detected (I-squared 68.4%, p=0.002), but a similar result was found when using a random-effects analysis (OR 4.79, 95% CI: 2.40, 9.58, p<0.001). A funnel plot suggested the possible presence of publication bias. Only 2 studies reported separate analyses for women with thrombophilic conditions who were using OCs: one found a significantly increased OR for CVT in women with hyperhomocysteinemia (OR 19.5, 95% CI: 5.7, 67.3), factor V Leiden (OR 30.0, 95% CI: 3.4, 263.0) and prothrombin mutation (OR 79.3, 95% CI: 10.0, 629.4), compared with control participants; the other reported an independent association between CVT, prothrombin mutation and OC use.