Women who have had their womb removed (hysterectomy) can safely be given oestrogen alone (with or without testosterone – see below). However, in the presence of the womb, oestrogen given as HRT will stimulate the lining of the womb (the endometrium) to thicken. In the absence of progesterone, this thickening continues, and over the course of time this may lead initially to irregular bleeding due to haphazard shedding of the endometrium, but more importantly cancer may develop in the endometrium (endometrial or womb cancer). In sequential HRT, the addition of progesterone results in the regular shedding of the endometrium, thereby preventing the development of endometrial cancer, and also irregular bleeding as the shedding of the endometrium is regulated. In the continuous combined formulation, the constant presence pf the progesterone prevents the thickening of the endometrium, and therefore again protects against the development of endometrial cancer.
Cyclical HRT is often prescribed to women who are having menopausal symptoms but are still having periods or for those whose periods stopped less than a year ago. Continuous HRT (without bleeds) is more suitable for women who have not had menses for more than one year.
The “hormone coil” or “hormone intrauterine device” (also known as the Mirena or the levonorgestrel intrauterine system) may also be used to protect the endometrium by preventing its thickening – in the menopausal woman there most often no bleeding, and oestrogen can be given without additional progesterone. The coil lasts for 5 years – visit here for further details.