Combined hormonal contraceptives are associated with a slightly increased risk of venous and arterial blood clots.[39] Venous clots, on average, increase from 2.8 to 9.8 per 10,000 women years[40] which is still less than that associated with pregnancy.[39] Due to this risk, they are not recommended in women over 35 years of age who continue to smoke.[41] Due to the increased risk, they are included in decision tools such as the DASH score and PERC rule used to predict the risk of blood clots.[42]