How Intrauterine Devices (IUDs) Work
Intrauterine devices (IUDs) primarily work by preventing fertilization through multiple mechanisms, with copper IUDs and hormonal (levonorgestrel) IUDs having distinct but overlapping modes of action. 1, 2
Types of IUDs and Their Mechanisms
Copper IUDs
- Create a spermicidal environment in the uterus and fallopian tubes through the release of copper ions
- Impair sperm function and movement, preventing them from reaching and fertilizing an egg 2, 3
- Can be used as emergency contraception when inserted within 5 days of unprotected intercourse (or up to 5 days after ovulation) 4
- Have a failure rate of less than 1% and can remain effective for up to 10 years (Paragard) 1, 3
Levonorgestrel IUDs (Hormonal)
- Release small amounts of the progestin hormone levonorgestrel locally in the uterus
- Thicken cervical mucus, creating a barrier that prevents sperm from entering the upper reproductive tract
- Thin the uterine lining (endometrium), making it less receptive to implantation
- Partially suppress ovulation in some women
- Have a failure rate of less than 1% with varying durations of effectiveness:
- Mirena: 5-7 years
- Kyleena: 5 years
- Liletta: 5 years
- Skyla: 3 years 1
Important Clinical Considerations
Effectiveness and Safety
- Modern IUDs are among the most effective reversible contraceptive methods available, with failure rates below 1% 1, 5
- Recent research suggests that both copper and hormonal IUDs primarily work by preventing conception rather than preventing implantation of a fertilized egg 2
- IUDs do not protect against sexually transmitted infections (STIs) or HIV 4, 1
- Consistent condom use should be recommended for women with IUDs who are at risk of STIs/HIV 1
Contraindications
- Pregnancy (Category 4 - unacceptable health risk) 4
- Current purulent cervicitis, active gonorrhea or chlamydia infection, current PID 1
- Uterine anomalies that distort the cavity 1
- High risk for STIs (Category 3 - risks usually outweigh benefits) 4
Non-Contraceptive Benefits
- Copper IUDs: Non-hormonal option for women who prefer or require hormone-free contraception
- Levonorgestrel IUDs: Significant reduction in menstrual bleeding, improvement in dysmenorrhea, and can be used for treatment of heavy menstrual bleeding 1
- Both types offer rapid return to fertility after removal 1
Insertion and Follow-up
- Proper insertion technique is essential and includes:
- Cleansing the cervix with antiseptic solution
- Using ring forceps to grasp the anterior lip of the cervix
- Ensuring high fundal placement of the device
- Confirming proper placement through bimanual examination or ultrasound 1
- Risk of pelvic inflammatory disease (PID) is highest in the first 20 days after insertion, then returns to baseline 1
Future Applications
IUDs are evolving beyond contraception to potentially address other women's health issues, including multi-purpose prevention technologies, hormone replacement therapy, endometriosis, uterine fibroids, and endometrial cancer 6.