The progestogen-only mini-pill

Abstract

A review is presented of the existing literature on the progestogen-only "mini-pill", a greatly under-used method of contraception. The under-use appears to stem from a lack of awareness on the part of medical advisers of the reasonable efficacy and minor side effects of the method. The benefits and disadvantages have been carefully evaluated and recommendations made for the more widespread use of progestogen-only mini-pills.

PIP: The progestogen-only minipill is used by few of the 50 million women worldwide who use oral contraceptives. This review deals mainly with minipills containing norethindrone (NET) 350 mcg or levonorgestrel (LNG) 30 mcg. The minipill exerts its antifertility influence at the endometrial, ovarian, tubal ephithelial, follicular, and luteal levels as well as on the cervix and cervical mucus. Although some earlier trials indicated pregnancy rates of 1.4-4.3/100 woman years, later combined pregnancy rates in trials of 5 different progestogen-only pills varied from .9-3 pregnancies/100 woman years. Recent indications show, in general large scale usage, minipill pregnancy rates similar to that of combined pills. Several small studies show an increase in the proportion of ectopic pregnancies in minipill users. Variability of menstrual cycle lengths is a controversial aspect of the minipill. In 2 studies using NET and norgestrel, 46-66% of cycles fell in the 25-35 day range. Vaginal bleeding lasted 4-6 days in 78% of cycles. 20-30% of patients notice spotting or breakthrough bleeding, which occurs in 5.8-16.2% of cycles. Intermenstrual bleeding problems are a major concern with progestogen-only methods, and prospects for avoiding the problem completely are limited. The progestogen-only minipill appears to cause no deterioration in carbohydrate tolerance, to have little or no effect on blood lipids and to cause no detectable change in liver function, blood clotting and platelet aggregation, thyroid function, or pituitary-adrenal responsiveness. There is no evidence linking LNG or NET used as a minipill to breast, cervix, or endometrium cancer. Progestogen may protect against endometrial cancer. No cases of congenital abnormality have been reported in babies born to women taking the minipill at conception. Progestogen tends to have no effect on breast milkvolume or may cause a slight increase. No effect of progestogen taken by the lactating mother has been demonstrated on the health or growth rate of the baby.