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Intrauterine devices (IUDs) are quickly becoming the HBICs of the contraception game. If you’re thinking about getting one, here’s everything you need to know:

1. There's more than one kind.

All IUDs are small, T-shaped devices that a doctor inserts through the cervix into the uterus. Each has a small string that goes from the cervix into the vagina, which a physician uses to remove the device. There are a number of IUD brands, each of which delivers different effects: ParaGard is non-hormonal. The copper coils on its frame cause a harmless inflammatory response that is toxic to sperm and eggs that lasts up to 10 years, or until you have the device removed.

Hormonal IUDs, like Mirena, Liletta, Kyleena, and Sklya, release a synthetic form of progesterone called progestin. This prevents pregnancy by thickening cervical mucus to keep sperm from entering the uterus and by thinning the uterine lining to stop a fertilized egg from implanting in the uterine wall. Depending on the brand, a hormonal IUD can be effective for three to six years, or until you have it removed, according to the Mayo Clinic.

2. They are 99 percent effective in preventing pregnancy.

IUDs are the most dependable birth control you can get, short of permanent sterilization, according to the Centers for Disease Control. Unlike the pill or condoms, this set-it-and-forget-it method leaves virtually no room for user error. The copper IUD is immediately effective; hormonal IUDs begin working right away if inserted during the first week of your cycle, which begins the day you get your period. When inserted outside this timeframe, you’ll need to use backup birth control such as condoms for seven days.

3. The copper IUD can be used as emergency contraception.

If inserted within five days of unprotected sex, it stops sperm from swimming well enough to reach an egg, according to Planned Parenthood. (Because hormonal IUDs function differently, they can not be used as emergency contraceptive.)

4. They don't prevent STIs.

Non-barrier methods like the IUD, birth control pills, emergency contraception, and subdermal implants will not prevent an infection from passing from partner to partner, according to Planned Parenthood. The only way to reduce your risk during sex is to use a female or male condom. And since exposure to STIs, like chlamydia and gonorrhea, may put you at an increased risk of pelvic inflammatory disease if you have an IUD, it’s especially important that you protect yourself, says Dr. Andrea Chisholm, OB-GYN, gynecologist at Cody Regional Health in Cody, Wyoming.

5. IUDs can be expensive upfront.

An IUD, plus insertion, can cost up to $1,300 out of pocket, according to Planned Parenthood. However, the Affordable Care Act requires insurers and employers (except those who object for moral or religious reasons) to cover IUDs and other birth control options without a copay. Be forewarned, though — some insurance plans cover the device and insertion, but not the doctor's visit to have the IUD removed, according to Bedsider.org. Check with your insurance or healthcare provider to see what an IUD costs from start to finish.

6. IUD insertion isn't pleasant.

"There is a pinch, followed by two big cramps, and then it's done. It’s very quick,” says Dr. Leah Torres, an OB-GYN and reproductive health specialist in Utah. "I would never tell someone, 'It's not bad,' or, 'It won't hurt.' "

While a prophylactic over-the-counter pain reliever can help, the amount of discomfort a patient feels during insertion depends on the provider's skill and the patient's tolerance and expectations, Dr. Torres says. You can expect some spotting for a few days after the procedure, but it shouldn’t be a period-like flow, says Dr. Yesmean Wahdan, gynecologist and associate medical director at U.S. Medical Affairs for Bayer Women’s HealthCare. If you experience heavy bleeding or cramping that lasts more than a few weeks, call your doctor to see what’s going on, she says.

7. IUDs are safe for teens.

"Given the efficacy, safety, and ease of use, LARC [long-acting reversible contraception] methods should be considered first-line contraceptive choices for adolescents," wrote The American Academy of Pediatrics in a 2014 statement. Thereafter, a Colorado program that distributed 30,000 IUDs to low-income women resulted in a 40 percent drop in the teen pregnancy rate over four years.

8. An IUD may change your vaginal discharge.

Women using copper IUDs complained more frequently about unusual or bad-smelling discharge than women using levonorgestrel-releasing IUDs, according to a 2014 study published in The European Journal of Contraception & Reproductive Health Care. That’s likely because the copper IUD causes inflammation, which is harmless but can increase secretions of white-yellow mucus from the cervix and possibly the uterus, Dr. Chisholm says. While the symptom may resolve itself as your body adjusts to the IUD, it could be your new normal. Either way: "This fluid should not smell bad. If at any time vaginal secretions have a foul odor and/or your vagina feels itchy or irritated, you should see your doctor to be sure you don't have an infection," she says.

9. Some IUD users don’t get periods.

Thanks to the synthetic progesterone in hormonal IUDs, which thins the lining of your uterus, cramping should become less intense while periods become lighter or nonexistent, according to Planned Parenthood. But the impact on your flow depends on which brand you choose, says Dr. Wahdan. "Generally, the higher the dose of hormones in the IUD, the more likely you are to experience amenorrhea, or absence of your period," Dr. Wahdan says. Clinical trials show that 20 percent of women using Mirena, 12 percent of women using Kyleena, and 6 percent of women using Skyla stop getting their periods within the first year of use, she says. Clinical trials also showed that 19 percent of women using Liletta stopped getting their period within the first year, 27 percent by the end of the second year of use, 37 percent by the end of the third year, and 41 percent by the end of the fourth.

10. An IUD can make your period worse.

"ParaGard's primary side effect is heavier period bleeding and more cramping, which commonly lasts for the first six months after insertion," says Dr. Cheryl Chastine of South Wind Women's Center in Wichita, Kansas. That’s because the copper IUD increases inflammatory factors, such as prostaglandins, which are normally produced by your uterine lining and are responsible for monthly period cramps, Dr. Chisholm says. And the more prostaglandins you have, the more cramping you might feel. That said, an NSAID like ibuprofen should help relieve them. "If you normally have very painful cramping with your period," Dr. Chisholm says, "the ParaGard IUD is probably not a good choice for you."

11. Your IUD might mess with your skin.

Hormonal contraception that contains progestin, such as hormonal IUDs, can increase circulating levels of male sex hormones known as androgens, which can overstimulate the skin’s oil glands and ultimately provoke pimples, Dr. Chisholm says. That said, research only shows an association between hormonal contraception and acne — so there’s no prove it causes breakouts or that it definitely will for you.

12. An IUD may improve your sex life.

An IUD won’t necessarily affect your desire for sex, ability to become aroused or orgasm, or the way sex feels, according to a 2012 Journal of Medicine study. However, the comfort of knowing you’re protected from pregnancy may empower you to have more spontaneous sex, as was the case for IUD users enrolled in 2014 study conducted by researchers at University of Wisconsin-Madison.

13. Your IUD string could poke your partner during sex.

In the same 2014 study, some women said their partners felt their IUD strings during intercourse, negatively impacting their time in bed. If yours complains he can feel the string, Dr. Wahdan suggests asking your doctor to trim or tuck it behind your cervix.

14. IUDs can raise your risk of yeast infections.

Several studies link IUDs with recurrent yeast infections, suggesting that the IUDs and their strings can harbor candida, a.k.a. yeast, and allow it to thrive, particularly if you’re susceptible to yeast overgrowth, Dr. Chisholm says.

15. It’s possible for an IUD to fall out — but it’s rare.

Expulsion is when the IUD passes out of the uterus through the cervix and into the vagina, but it only happens to 2 to 10 percent of all IUD users, according to the American College of Gynecologists. If your IUD has migrated out of your uterus, you’ll feel cramping, have pain during sex, and might experience an increase in discharge, Dr. Chisholm says. If you have these symptoms or think your IUD has moved, see your doctor right away, since an IUD expulsion increases your risk of pregnancy.

16. Your IUD can poke through your uterus.

In fewer than 2 in every 1,000 women who get IUDs, the device adheres to or perforates the uterus wall, which can potential injure other organs, according to a 2015 study published in the journal Contraception. Although this typically occurs when a doctor places the IUD incorrectly, which can compromise its ability to prevent pregnancy, "it’s usually not discovered until the patient comes in with pain or a pregnancy," Dr. Chisholm says. A perforation can lead to intense pain and cramping that doesn’t get better over time. If you experience these symptoms after an IUD insertion, and an NSAID pain reliever such as ibuprofen doesn’t help, head back to your doctor’s office, and use condoms until your MD confirms the device is still in place.

17. It's OK to leave your IUD in past its prime.

Every IUD has a designated lifespan, at which point, you’ll need a doctor to remove it. "Leaving an IUD in place past the approved time shouldn’t cause an infection or damage, so it's not necessary to rush to the doctor to have it removed immediately after it expires," Dr. Chastine says. While studies suggest that both ParaGard and Mirena are effective at preventing pregnancies for at least two years beyond the FDA-approved period, it’s smart to use a back-up birth control method, Dr. Chastine says.

18. Your IUD won’t affect your long-term fertility.

There’s no difference in pregnancy rates among former IUD users and former users of other contraceptive methods, according to one study published in The European Journal of Contraception & Reproductive Health Care. It doesn’t matter how long you’ve had your IUD — once it’s out, it’s possible to get pregnant right away.

Additional reporting by Robin Marty.

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Ashley Oerman
Contributing Writer

Ashley Oerman is a contributing writer at Cosmopolitan, covering fitness, health, food, cocktails, and home. You can follow her on Instagram @AshleyOerman. She is pro-carbs.