Abstract
BACKGROUND: The study was conducted to determine the impact of switching from oral to transdermal patch or vaginal ring contraception on biomarkers of thrombosis. STUDY DESIGN: Current healthy oral contraceptive (OC) users were randomized to switch to either a contraceptive ring (CR) or patch (CP) and underwent phlebotomy to measure surrogate biomarkers of thrombosis [sex hormone-binding globulin (SHBG), free protein S and activated protein C resistance (APC-r)] before switching, and during the fourth cycle of use of the new method. RESULTS: Of 142 reproductive age women enrolled, 120 sample pairs were available for analysis. SHBG increased significantly from baseline in CP users [mean change (95% CI), +29.9 nM (9.6-50)] but not in CR users [-1.6 (-16.6 to 13.5)]. Protein S decreased significantly from baseline in CP users [mean change -7.1% (-12.1 to -2.1)], but increased significantly in CR users [+5.3% (1.1-9.6)]. The APC-r ratio did not undergo a significant change from baseline in either group [CP +0.06 (-0.06 to 0.18), CR +0.02 (-0.10 to 0.14)]. Compared to CR users, subjects using the CP had significantly higher SHBG [187.5 (167.0-208), 146 (132.6-159.4), p=.012], significantly lower protein S [81.8 (76.8-86.8), 93.6 (89.1-98.1), p=.001] and similar APC-r ratios [2.99 (2.85-3.14), 3.09 (2.96, 3.22), p=.3] at the Cycle 4 visit. CONCLUSION: OC users who switch to the ring exhibit beneficial changes in biomarkers of thrombosis, while those switching to the patch display a shift favoring clot formation.