Yes, it's oestrogen related.
It's swings and roundabouts time: you have a slight increase in your blood clot risk (about 60 vs 30 non-users in 100,000 women over a year, most of whom don't die as a result) but pregnant women have a greater still risk (somewhere between 100 and 200 per 100,000 women) and you also are less likely to get ovarian and endometrial cancers.