This guideline warns that combined hormonal contraceptives when used in ring and patch form may have a higher risk of VTE than the normal pill. Patients should be warned of this. The absolute risk of VTE is still very low.
Compared to no contraceptive use, the COC has a relative risk (RR) of 3.2, the patch of 7.9 (absolute risk 9.7 per 10,000 exposure years) and the ring 6.8 (absolute risk 7.8 per 10,000 exposure years).
When you compare them to levonorgestral containing COC pills, the patch has RR of 2.3 (though not significant) and the ring of 1.9 (significant).