Table 4.

 Characteristics of included observational studies on hormone replacement therapy that reported venous thromboembolism

Reference	Route of oestrogen administration	Clinical end point	Oestrogen type	Definition for current users*	No of exposed cases	Adjusted risk ratio of venous thromboembolism (95% CI)
Boston CDSP 1974w21	Oral	First episode of idiopathic venous thromboembolism	Mainly conjugated equine oestrogen	Not available	3	1.9 (1.4 to 7.8)
Daly 1996w1	Oral; transdermal	First episode of idiopathic venous thromboembolism	Estradiol (or estradiol valerate) or conjugated equine oestrogen; estradiol or estradiol valerate	<1	37; 5	4.6 (2.1 to 10.1); 2.0 (0.5 to 7.6)
Jick 1996w3	Oral	First episode of idiopathic venous thromboembolism	Conjugated equine oestrogen or esterified oestrogen	<6	21	3.6 (1.6 to 7.8)
Nurses’ health study 1996w4	Oral	First episode of pulmonary embolism	Mainly conjugated equine oestrogen	Not available	68	2.1 (1.2 to 3.8)
Perez-Gutthann 1997w5	Oral; transdermal	First episode of idiopathic venous thromboembolism	Estradiol (or estradiol valerate) or conjugated equine oestrogen; estradiol or estradiol valerate	<6	20; 7	2.1 (1.3 to 3.6); 2.1 (0.9 to 4.6)
Smith 2004w9	Oral	First episode of venous thromboembolism	Conjugated equine oestrogen; esterified oestrogen	Not available	121; 86	1.7 (1.2 to 2.2); 0.9 (0.7 to 1.2)
Douketis 2005w10	Oral; transdermal	First episode of idiopathic venous thromboembolism	Not available; not available	<1	36; 3	1.9 (1.2 to 3.2); 0.8 (0.3 to 2.8)
ESTHER 2007w11	Oral; transdermal	First episode of idiopathic venous thromboembolism	Estradiol (or estradiol valerate) or conjugated equine oestrogen; estradiol or estradiol valerate	<3	57; 67	4.5 (2.6 to 7.5); 1.1 (0.8 to 1.7)

*Duration (months) between oestrogen use and venous thromboembolism.