MidLife
Why does the WHI study only one type of estrogen/progestin?
The hormone component is studying the effects of one type of estrogen (conjugated equine estrogens, Premarin) and one type of progestin (medroxyprogesterone acetate, MPA). The choice of these hormones was made on the basis of science and public health. The recorded experience of women who used Premarin and MPA is what prompted the need for a rigorous clinical trial, and the initial public health question to be answered is whether the hormones most commonly used by women have benefits that exceed their risks.
Recruitment of more than 27,000 women was successful, but arduous. For each additional therapy chosen, it would be necessary to recruit at least 14,000 additional women. WHI investigators therefore, adopted a more feasible strategy that would not add to the cost of the study. The WHI is obtaining a full accounting of all hormones used during the course of the study as well as in the past by the more than 161,000 women currently enrolled in the WHI. Each variety of hormones used by the women can then be related to their future health status, and compared to the results in the clinical trial of the subset of 27,000 women. In this manner, the effect of other hormone therapies can be estimated.
Source: The National Heart, Lung and Blood Institute
