Estrogen Plus Progestin Doubles Risk of Venous Thrombosis

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Estrogen Plus Progestin Doubles Risk of Venous Thrombosis

Charlene Laino

Dec. 15, 2003 (San Diego) ‹ The use of estrogen plus progestin doubles the

risk of venous thrombosis in women, according to a new analysis of data from

the Women's Health Initiative.

" Body mass index and older age were the primary determinants of increased

risk, " Cushman, MD, from the University of Vermont in Burlington, told

a press briefing here at the 45th annual meeting of the American Society of

Hematology.

Also, in a nested case control study, the researchers found that factor V

Leiden was the primary genetic factor associated with increased thrombosis

risk.

The primary analysis included 16,608 women aged 50 to 79 years who were

randomized to receive either 0.625 mg per day of conjugated equine estrogen

and 2.5 mg per day of medroxyprogesterone acetate, or placebo.

At about five years of follow-up, when the trial ended early after the risks

of estrogen plus progestin were found to outweigh its potential benefits,

the study showed that women in the estrogen plus progestin group had

approximately a twofold increased risk of developing venous thrombosis

compared with those receiving placebo.

At baseline, women in both groups were at similar risk for thrombosis, Dr.

Cushman said. About one third of the women were aged 50 to 59 years,and 22%

were aged 70 to 79 years; 84% were white; 35% had a body mass index (BMI) of

25 to 29; and one third had a BMI of 30 or higher.

Overall, 167 women in the estrogen plus progestin group developed thrombosis

compared with 76 women in the placebo group. " This translated to a 2.1-fold

increased risk, which was significant, with a 95% confidence interval [CI]

of 1.6 to 2.7, " Dr. Cushman said.

The risk was similar for deep vein thrombosis and pulmonary embolism, she

added. Also, women appeared to be at greatest risk during their first year

of taking estrogen plus progestin, when risk was increased fourfold, she

said.

The nested case-control study included 147 women who developed thrombosis

and 513 controls. Nearly 14% of cases tested positive for factor V Leiden

compared with about 5% of controls, Dr. Cushman reported.

That translated to a 6.7-fold increased risk of thrombosis associated with

factor V Leiden (95% CI, 3.1 - 14.5), she said.

" Factor V Leiden, inactivated at a rate approximately 10 times slower than

normal factor V, increases a woman's risk for venous thrombosis, " she said.

Brenner, MD, associate professor of medicine at the Technion-Israel

Institute of Technology in Haifa, and a specialist in thrombosis, said the

findings " offer insights into which women are at increased risk of venous

thrombosis. "

Further studies are needed before physicians start testing for factor V

Leiden prior to prescribing estrogen plus progestin, however, he said.

ASH 45th Annual Meeting: Abstract 719. Presented Dec. 9, 2003.

Reviewed by D. Vogin, MD