‘Don’t take the pill if you have a serious clotting disorder’

Thrombosis is a rare side-effect of taking the contraceptive pill. The risk of thrombosis for a woman who takes the pill can increase if she has a serious hereditary clotting disorder or if her mother or sister has developed thrombosis. These are the results of research conducted by Liesbeth van Vlijmen of the University Medical Center Groningen. She would advise women with a serious clotting disorder against taking the pill, and would also recommend that women with a family history of thrombosis receive proper advice about alternative forms of contraception. She will be awarded a PhD by the University of Groningen on 17 February.

Van Vlijmen’s research focuses on the link between taking the pill and the risk of thrombosis, and the effect of other risk factors for thrombosis. She also studied the effect of a mother or sister who has had thrombosis.

Thrombosis as a result of taking the pill is rare, occurring just 5-12 times per 10,000 ‘pill years’. The risk of thrombosis depends on the length of time that a woman takes the pill and the dosage. In her research, Van Vlijmen shows that the risk of thrombosis rises sharply in women with a serious hereditary clotting disorder (deficiency of antithrombin, protein C, or protein S) when they take the pill. She would advise this group of women against taking the pill as a form of contraception.

Van Vlijmen’s research also reveals that the risk of thrombosis rises slightly in women with a mild hereditary clotting disorder (Factor V Leiden or prothrombin-G20210A mutation) when they take the pill. These women are, however, at a much greater risk during pregnancy than when they are taking the pill. Van Vlijmen advises that this group of women should get counseling on all forms of contraception, including the pill. The risk of thrombosis and the reliability of alternative forms of contraception, and any other risk factors, should be discussed. Women can then choose the most suitable method of contraception.

Having a mother or sister who has had thrombosis while taking the pill or during pregnancy is another potential risk factor that women should take into account. According to Van Vlijmen, this can double or trible the basic risk. Van Vlijmen would therefore recommend raising this subject when discussing these women’s options.

According to Van Vlijmen it will always be difficult to predict which women will develop thrombosis while taking the pill. Her research of the characteristics of the women who do develop thrombosis while on the pill shows that most of them also had other thrombosis risk factors. A clotting disorder, a family history of thrombosis or serious obesity were the most common. In addition, many of the women who developed thrombosis while on the pill, had taken the pill previously and been pregnant.

Van Vlijmen recommends women and GPs to be more aware of the possibility of thrombosis while taking the pill, even in young women. Van Vlijmen: ‘The earlier thrombosis is diagnosed, the sooner appropriate treatment can be started.’

Curriculum Vitae

Lies van Vlijmen (Naarden, 1958) studied Medicine at the University of Groningen. She carried out her PhD research in the Haemostasis and Thrombosis research group of the Department of Haematology at the University Medical Center Groningen. Her research was partly funded by the Netherlands Organization for Health Research and Development (ZonMw) and the Netherlands Heart Foundation. As well as carrying out this research, Van Vlijmen also works as a senior clinical assessor for gynaecological drugs at the Dutch Medicines Evaluation Board (CBG) and the European Medicines Agency (EMA).