Clinical features

Why?

• It increases the risk of developing venous thromboembolism. ^b
• Third-generation oral contraceptives are slightly more dangerous than second generation. ^b
• There is no clear evidence to suggest that women on HRT are at increased risk of venous thromboembolism. ^a

Oral contraceptive pill increases the risk of venous thromboembolism very slightly

Patient	Prognostic Factor	Outcome	CER	OR (95% CI)	NNF+ (95% CI)
healthy a	oral contraceptive pill independent	venous thromboembolism at weeks	0.003%	2.4 (1.6 to 3.5)	6000 (3400 to 14000)

Third generation contraceptives increase the risk of venous thromboembolism slightly more than second generation

Outcome	Risk Factor	PEER	OR (95% CI)	NNH (95% CI)
venous thromboembolism b	desogestrel or gestodene compared to levnogestrel independent	0.012%	2.2 (1.0 to 4.7)	7000 (2300 to infinity)

Patients with factor V Leiden who take an oral contraceptive are at greatly increased risk of venous thromboembolism

Outcome	Risk Factor	PEER	OR (95% CI)	NNH (95% CI)
venous thromboembolism b	oral contraceptive and factor V Leiden not independent	18%	34.7 (7.8 to 154)	140 (32 to 700)