From the Research
The presence of a dominant follicle with a levonorgestrel-releasing intrauterine system (Mirena IUD) is generally not concerning and requires no specific intervention. Dominant follicles, which are ovarian cysts that develop as part of the normal menstrual cycle, can still form even with a Mirena IUD in place because this type of IUD does not consistently suppress ovulation in all users 1. While the Mirena primarily works by thickening cervical mucus and thinning the uterine lining to prevent pregnancy, about 25-50% of women using it will continue to ovulate regularly. These functional ovarian cysts are typically benign, asymptomatic, and resolve spontaneously within 1-3 menstrual cycles. If a dominant follicle or ovarian cyst causes symptoms like pelvic pain or irregular bleeding, over-the-counter pain relievers such as ibuprofen (400-600mg every 6 hours as needed) can help manage discomfort. Only persistent cysts (lasting more than 2-3 months) or those causing severe symptoms would warrant further evaluation by a healthcare provider. The Mirena IUD remains highly effective at preventing pregnancy (over 99%) regardless of whether ovulation occurs, so there is no need to use backup contraception when dominant follicles are present. However, it's essential to note that the risk of ectopic pregnancy, although low, may be higher with lower-dose levonorgestrel-releasing intrauterine systems, as suggested by a recent study 2. In the context of a dominant follicle with an IUD, the focus should be on monitoring for any symptoms that could indicate a complication, such as severe pain or heavy bleeding, rather than the presence of the follicle itself. Given the most recent and highest quality evidence, the primary concern with an IUD in place, including the development of a dominant follicle, is the extremely low but potential risk of ectopic pregnancy, which should be considered in the overall management plan 3, 2.