Body Health

Study looks at oral contraceptive pill blood clot risk

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contraceptive pillA new international study into the safety of oral contraceptive pills has found no significant difference in risk between different types of birth control pill.

This is good news for New Zealand women following suggestions that some contraceptive pills, such as Yaz and Yasmin, may increase risks of blood clots more than other contraceptive pills.

The study

Known as the International Active Surveillance Study of Women Taking Oral Contraceptives (INAS-OC), the study analysed data from more than 85,000 women in the United States and Europe.

It is the largest study to date to investigate the safety of oral contraceptive pills and, importantly, to look at the number of venous blood clots also known as VTEs (venous thromboembolism) occurring on pills containing different progestins.

VTE is a rare and potential life threatening event. For women the risk of developing a VTE is dependent on a number of factors. Some of these include age, being overweight and obese, having given birth in the last few weeks or having a positive family history. Having major surgery or trauma, prolonged immobilisation or a long haul flight are also risk factors.

In addition, it has been known for some time that taking the oral contraceptive pill increases the risk of VTE due to the oestrogen component. However, evidence has been conflicting as to whether different progestins in the pill confer different risks.

What the study has shown

‘We now have definitive evidence from this large, multicentre, prospective study that there is no difference in risk of thromboembolic events for the different progestins used in the combined oral contraceptives,’ says Dr Meyer, an Auckland gynaecologist and obstetrician.

‘For women assessed to be appropriate candidates for the use of the combined oral contraceptive, it is reassuring to know that drospirenone-containing combined oral contraceptives can safely be given as an option,’ Dr Meyer adds.

Other facts

  • Some research studies have indicated there may be an increased risk of blood clots associated with some types of oral contraceptive pills that contain oestrogen.
  • Blood clots are a rare complication of taking oral contraceptives. Symptoms may include tenderness in the calf muscle, swelling or redness in the lower leg, mild fever, or cramping/pain – usually in the calf muscle area. If a blood clot is suspected, it’s important to seek medical attention as soon as possible.
  • Medsafe advises that women can also have blood clots when not taking oral contraceptives and that in a year, approximately 5-10 women in every 100,000 aged 15-44 who are not taking the pill will develop blood clots.
  • Drospirenone is a synthetic hormone found in combination birth control pills. There has previously been concern that oral contraceptives containing drospirenone have a higher blood clot risk than other birth control pills.

Image / NZ Real Health

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