The pill may potentially increase the risk of blood clots and pulmonary embolism

Taking a third-generation contraceptive pill may increase the risk of suffering from a pulmonary embolism, an ischemic stroke or a myocardial infection, a team of scientists has claimed. Past studies have shown that taking combined oral contraceptives is associated to a higher risk of venous and arterial thromboembolism – or blood clots – which can be responsible for these adverse health events.

Most birth control pills contain two main compounds, a form of oestrogen and progesterone-like compounds called progestins. Both are similar to female reproductive hormones, oestrogen and progesterone. The contraceptive effect from the pill comes mainly from the progestins in the pill.

This latest research, published in the BMJ, identifies the risks associated with eight different combinations of oestrogen and synthetic progestogen doses. It suggests that third generation pills which contain two types of progestins – desogestrel and gestodene – come with higher risk of pulmonary embolism.

4.9 million women researched

The researchers decided to assess the risk of taking one of the eight reimbursed oral contraceptives in France, depending on the type of progestins and dose of oestrogen they contained. The objective was to identify which combination was associated with the lowest risk of venous and arterial thromboembolism – and therefore making pulmonary embolism, ischemic stroke, and myocardial infarction more likely.

In total, the researchers analysed the medical data of 4.9 million women aged 15-49 years, living in France, with at least one reimbursement for oral contraceptives between July 2010 and September 2012. During the two-year period, 1800 pulmonary embolisms, 1046 ischemic strokes and 407 myocardial infarctions occurred.

Analysing these figures, the scientists came to the conclusion that the so-called third generation pills composed of esogestrel and gestodene were associated with higher relative risks for pulmonary embolism – more than twice as much than for second-generation pills containing levonorgestrel, another synthetic progestogen.

Combining levonorgestrel and oestrogen

Among second-generation pills, levonorgestrel combined with 20 µg oestrogen was associated with a statistically significantly lower risk than levonorgestrel with 30-40 µg oestrogen for each of the three serious adverse events, and appeared the safest for women.

"Levonorgestrel with 20 µg of oestrogen was globally associated with a lower risk of the composite endpoint of hospital admission for pulmonary embolism, stroke, or myocardial infarction compared with the other oral contraceptive combinations tested", the researchers say.

These findings are consistent with those revealed in past research: they also point out that the risk of suffering from pulmonary embolism, ischemic strokes or myocardial infections increase with the age of the woman. However, women should note that the risk remains low, whichever pill they are on.