The levonorgestrel intrauterine system in contraception

The levonorgestrel intrauterine system (LNG IUS) releases 20 mug/24 h of le vonorgestrel from a polymer cylinder mounted on a T-shaped frame and covere d with a release rate-controlling membrane. It is approved for 5-year use. The most outstanding features of LNG IUS are its high contraceptive efficac y and reduction of menstrual blood flow. No single mode of action can accou nt for its contraceptive efficacy. The endometrium becomes thin and inactiv e, and the cervical mucus turns scanty and viscous. Although ovulation may be disturbed to some degree, estradiol production continues normally. The P earl index for LNG IUS from large clinical trials is 0.1. Extrauterine preg nancies occur in 1 in 5000 users per year. Both the volume of menstrual blo od loss and the number of bleeding days are reduced. During the first year of use, 20% of women become amenorrheic. There is an initial increase in th e mean number of bleeding and spotting days, but in 3 to 6 months the numbe r of bleeding and spotting days is the same as observed in copper IUD-users . The variation between individuals is wide and unpredictable. There are al so additional health benefits secondary to the inactivation of the endometr ium: increased hemoglobin, decreased dysmenorrhea, a possible decrease in p elvic inflammatory disease. LNG IUS may also decrease the growth of fibroid s. LNG IUS is well accepted by users, with typical annual continuation rate s above 80% in clinical studies. (C) 2000 Elsevier Science Inc. All rights reserved.