Mirena IUD (IntraUterine Device) is placed in the uterus where it constantly releases progestin hormone called levonorgestrel. Levonorgestrel reduces the frequency of ovulation, thins the endometrium, and changes the cervical mucus to obstruct passage of sperm through the cervix. Although the rate for unwanted pregnancies when using Mirena is very low, it is still possible to get pregnant.


All the hormone-containing products have a low chance for pregnancy but the chances are never reduced to zero. The only 100% secure method to prevent pregnancy would have to be to prevent spermatozoids from reaching the egg which is already prepared for fertilization.


The hormone released from Mirena does not affect the rate of false positive or false negative results in home pregnancy tests because they measure Beta HCG which is a hormone that is mainly produced by the placenta and does not depend on the levels of female sex hormones in the blood.