Venous thrombosis is a collective term for DVT (deep vein thrombosis) and pulmonary embolism. The researchers explained that most studies have focused on the clot risk for females on oral contraceptive pills. There are very few studies that focus on other contraceptives; referred to as non-oral hormonal contraceptives.
Non-oral hormonal contraceptives release hormones into the body more continuously.
Professor Øjvind Lidegaard and colleagues set out to determine what health effects, specifically venous thrombosis, non-oral hormonal contraceptives have on Danish females aged between 15 and 49 years, dating from 2001 to 2010. None of the women in the study were pregnant or had any medical history of cancer or blood clots before the study started.
They took into account a number of factors which could distort the findings, including the women's education level and their age.
Non-oral hormonal contraceptives, such as the vaginal ring, are linked to a higher risk of developing blood clots, compared to oral contraceptive pills
Over a period of 9,429,128 observation years, a total of 3,434 diagnoses of first-time venous thrombosis were made. The authors reported the following findings for females aged from 15 to 49 years:
- 2 venous thrombosis events per 10,000 exposure years for those not using any type of hormonal contraception
- 6.2 venous thrombosis events per 10,000 exposure years for those on a levonorgestrel-containing combined oral contraceptive pill
- 9.7 venous thrombosis events per 10,000 exposure years for those using a contraceptive skin (transdermal) patch
- 7.8 venous thrombosis events per 10,000 for those using a vaginal ring
- Women using a progestogen-only subcutaneous implant were found to have a slightly higher chance of blood clots
- Women using a progestogen-only intrauterine device either had no higher risk at all, or possibly a lower risk
The researchers worked out that of the women they studied, 2,000 of the vaginal ring users and 1,250 of the skin patch users should switch over to a combined levonorgestrel-containing oral pill to reduce the risk of a venous thrombosis event in one year.
Written by Sarah Glynn B.A. (Psych)