Can progestin be limited to every third month only in postmenopausal women taking estrogen?

We evaluated whether a progestin, added for 14 days every 3 months to estrogen replacement therapy, is capable of preventing the development of endometrial hyperplasia in postmenopausal women during a treatment period of 2 years. Postmenopausal women (263) in 10 hospitals and medical centers in Finland participated in this non-randomized prospective multicenter trial. The women received estradiol valerate 2 mg daily for 84 days and 20 mg of medroxyprogesterone acetate daily for days 71-84 followed by seven drug-free tablets. This regimen was repeated four times per year. The first year of treatment was completed by 227 (86%) women and the second year by 143 out of 146 women. The incidence of unscheduled and heavy bleedings was higher in women who were postmenopausal for less than 3 years. Endometrial biopsies demonstrated progestational response in 64% at 12 and 24 months, respectively. The 3 month regimen prevented development of endometrial hyperplasia but was not able to restore a hyperplastic endometrium to normal.