Study looks at risk of blood clots with progestin-only contraceptive methods (AUG 2012)
- A meta-analysis in
the British Medical Journal
compared the risk of blood clots (deep vein thrombosis and pulmonary embolism) in women using progestin-only contraceptives (e.g. Mirena® IUD,
progestin-only pills, Depo Provera® injection) to women who were not using hormonal contraception. The analysis included 8 observational studies (5 case-control, 3 cohort).
- Overall, the risk of blood clots was not significantly increased by progestin-only contraceptives (RR users vs nonusers - 1.03, [95% CI 0.76 to 1.39])
- Progestin-only pills did not significantly increase the risk of blood clots (RR users vs nonusers 0.90 [95% CI 0.57 to 1.45])
- The progesterone IUD (e.g. Mirena®) did not significantly increase the risk of blood clots (RR users vs nonusers 0.61, [95% CI 0.24 to 1.53])
- Progesterone injections (e.g. Depo Provera®) did significantly increase the risk of blood clots (RR users vs nonusers 2.67, [95% CI 1.29 - 5.53])
- The risk of blood clots from combined oral contraceptives has long been thought
to be associated with the estrogen component of the pills, although there has been some controversy that newer generation progestins
(see drospirenone) may also increase the risk
- This study found no increased risk of blood clots with progestin-only pills and progestin IUDs. The observational design of the studies included in the meta-analysis
limits the ability to draw firm conclusions regarding progesterone and VTE risk.
- The progesterone injection (e.g. Depo Provera®) was found to increase the risk for blood clots, but confounding is a concern since progesterone injections are often used to
control heavy menstrual bleeding in obese women, and obese women are at greater risk for blood clots. Selection bias is also a possibility if women who were at greater risk for blood clots were
given the progesterone injection instead of combined oral contraceptives.
- For more information on oral contraceptives, see oral contraceptive review