Birth control pills, patches and rings typically contain an estrogen and a progestin component. It has long been known that estrogen-containing birth control preparations (pill, patch, ring) increase the risk for blood clots (DVT, PE). This risk is partially due to the estrogen. However, part of the risk for clots is also due to the type of progestin in these preparations. This first became clear when it was found that so-called 3rd generation contraceptives (those containing the progestin called desogestrel) have about two times higher a risk for DVT and PE that so-called 2nd generation pills.