Mirena, a levonorgestrel-releasing intrauterine system (LNG-IUS), is a long-acting reversible contraceptive (LARC) device. This small, T-shaped device is placed inside the uterus by a healthcare provider. Its primary purpose is to prevent pregnancy for an extended period, offering a convenient and highly effective birth control option.
Mirena’s Effectiveness and How It Works
Mirena is a highly effective method for preventing pregnancy, boasting an effectiveness rate of over 99% for up to eight years. Less than one in 100 women using Mirena will experience a pregnancy in a year. However, no birth control method, short of abstinence or surgical sterilization, is 100% effective.
The Mirena IUD prevents pregnancy through several mechanisms, primarily by releasing a continuous low dose of the hormone levonorgestrel directly into the uterus. This progestin thickens the cervical mucus, preventing sperm from reaching an egg. It also thins the lining of the uterus, making it less receptive to a fertilized egg for implantation. In some individuals, Mirena may also partially suppress ovulation, meaning the ovaries do not release an egg.
Recognizing Pregnancy Signs While Using Mirena
Identifying pregnancy symptoms while using Mirena can be challenging because the device itself alters menstrual cycles. Many individuals experience lighter periods, irregular bleeding, or even a complete cessation of periods after a year of Mirena use. These changes can mask typical early pregnancy signs like a missed period.
Common early pregnancy symptoms can still occur. These include nausea, fatigue, breast tenderness, headaches, and mild cramping. If any of these symptoms arise, especially alongside unusual pelvic pain or changes in vaginal discharge, take a home pregnancy test. Consulting a healthcare provider is advised if there are concerns about a possible pregnancy or if the IUD strings feel shorter or longer than usual.
If Pregnancy Occurs with Mirena
If pregnancy is confirmed with Mirena in place, immediate consultation with a healthcare provider is necessary. This situation carries an increased risk of complications, including ectopic pregnancy, where the fertilized egg implants outside the uterus, most commonly in a fallopian tube. Approximately half of pregnancies that occur with Mirena in place are likely to be ectopic, which is a medical emergency.
The healthcare provider will assess the location of the pregnancy and the IUD. If the pregnancy is intrauterine and the IUD strings are visible, Mirena removal is generally recommended. Leaving the IUD in place increases the risk of miscarriage (ranging from 48% to 77%), preterm labor, and serious infections. While IUD removal itself can carry a risk of miscarriage (around 20%), this risk is lower than if the device is retained. If the strings are not visible, specialized procedures like ultrasound-guided removal may be considered to minimize risks.