A number of devices can be implanted within the uterus to prevent pregnancy for years at a time. After removal, which can occur at any time, ovulation quickly resumes and you can potentially get pregnant right away. This is a big advantage over progesterone injections, which can take months – or even a year or more – to wear off. 

Intrauterine Device (IUD) is a scary-sounding name, but it’s a popular option for long-acting, reversible birth control. The device is a little plastic “T” that sits in the uterus for up to five years, slowly releasing low levels of either progesterone or copper into the uterus. It’s just over an inch long and has two plastic strings hanging off the bottom. The strings hang just outside the cervix (not outside the vagina) for easy removal later on.

They work in two ways: the physical presence of the IUD in the uterus, plus the effect of the medication on the uterine lining. In terms of its physical presence, any device in the uterus causes a low level of inflammation, which is toxic to sperm and eggs. It also impairs implantation. 

The addition of progesterone or copper also prevents pregnancy. Copper increases inflammation (just in the uterine lining, not around the body), slows down sperm, and – if all else fails – impairs implantation. There has been some concern that copper IUDs “cause abortions” every cycle, but this is highly unlikely. The general consensus is that they work primarily by preventing fertilization rather than just preventing implantation. However, to be completely honest, nobody’s exactly sure how exactly copper IUDs work. They just do (1).

Conversely, the way progesterone IUDs work is well understood. In addition to the inflammation the device causes, progesterone thickens the mucus plug in the cervix (which blocks sperm from entering the uterus) and thins the lining of the uterus to prevent implantation. By and large, neither type of IUD prevents ovulation. Instead, it disrupts the viability of sperm, eggs, and embryos. 

As with hormonal contraception, there is a possibility that fertilization of an egg can occur with an IUD in place, which is why some Christians avoid IUDs altogether. 

One of the main advantages of IUDs is how effective they are. Over 99% of couples with an IUD won’t get pregnant over the course of the year. That’s more effective than any other non-permanent method of birth control.

Other benefits:

• No regular maintenance, no pills, no regular doctor visits

• Long-lasting: the same device prevents pregnancy for five years or more

In terms of cost, IUDs can be pricey, especially progesterone. However, the overall cost of an IUD is less expensive than The Pill; they pay for themselves after two years of not buying hormonal birth control.

The biggest downside of IUDs is the insertion. It involves a speculum exam, like a pap smear, but the instruments go further. A doctor dilates the cervix (painful) and inserts the applicator (a plastic tube, about the diameter of a drinking straw). The IUD is positioned in the uterus and the applicator comes out. There’s usually bleeding for a day or two, which can vary from light spotting to a heavy period. Serious complications are uncommon. The whole procedure by an experienced doctor takes less than a few minutes. If you’ve ever delivered a baby vaginally, the insertion is usually less painful.

Sometimes IUDs fall out, often within the first month. This happens in up to 6% of cases. Occasionally IUDs don’t align themselves correctly in the uterus, that is, they become mispositioned. This happens in about 10% of cases, causing pain and irregular bleeding. If this happens, the IUD needs to come out. It’s a hassle. Whether an IUD falls out on its own or gets removed by a doctor, it’s no longer sterile and needs to be replaced.

Whenever a couple wants to start trying for pregnancy, a doctor performs another speculum exam and pulls the IUD out (relatively pain-free). After that, the couple is good to go. The birth control is rapidly reversible. However, sometimes the strings retract into the uterus and minor surgery is needed to fish it out.

That being said, if a woman manages to get pregnant with an IUD in place, it may cause problems during the pregnancy. If it’s early in the pregnancy, your doctor may opt to pull the IUD out, but it can also be left in place if the risks of removal outweigh the benefits. It’s not the end of the world to get pregnant with an IUD in the uterus – many obstetricians will deliver a healthy baby with an IUD embedded in its placenta sometime in their career. 

In terms of side effects, bleeding and cramping are most common, especially in the first few months. Most women feel fine after six months. Sometimes the plastic strings can cause problems. They hang just outside the cervix and can feel pokey. If they’re too long, they can poke into the vaginal wall, in which case they can be trimmed shorter. If they’re too short, the penis can get poked during intercourse – not fun for your husband. To fix this, a doctor can try to push the strings aside or they can be cut flush with the cervix. 

Progesterone IUDs come in various doses. The most common one lasts five years, but lower dose IUDs may only be good for three years. In addition to birth control, progesterone IUDs improve painful, crampy periods. Many women find their periods get lighter, shorter, and less crampy with a progesterone IUD in place. Sometimes your period can disappear altogether for six months or more. Intermittent spotting is common but rarely dangerous. 

Copper IUDs are the same size and shape as progesterone IUDs. Unless you have an allergy to copper (rare), any female with a healthy uterus can get one. They tend to be less expensive, but not many doctors recommend them because they usually make periods heavier and more crampy. This often improves over the first six months, but if heavy periods are already a problem for you, a copper IUD may not be a good choice.

Overall, if you can get past the miserable insertion, IUDs are well-tolerated, low maintenance, and highly effective.

FOOTNOTES

(1) The lack of a definitive explanation on how a medical intervention works can be unnerving. However, to put it in perspective, the same issue exists with the medication acetaminophen (also called paracetamol, or Tylenol). It relieves fever and mild pain, likely through inhibiting inflammation in the body, but nobody’s really sure how. It just works, and it’s one of the most commonly used medications worldwide. Chances are you’ve taken it yourself.