• 132 Harley Street London W1G 7JX


The Intra-Uterine Device (IUD) and Intra-Uterine System (IUS) look and sound so similar that it is easy to confuse them. However, these two forms of contraception use very different methods to prevent you from getting pregnant. It’s important to understand these differences so that you can choose the right option for you.

How Similar Are the IUD and IUS?

You can tell how similar the IUD and IUS are just by looking at pictures of the two devices or comparing their full names. Both include the term Intra-Uterine, which means that they sit inside your uterus. The two devices look very similar too. They are both small, T-shaped and made out of plastic.

Another similarity between the two devices is the way they are fitted. If you want to use either of these options for contraception, it will need to be put in place by a doctor or nurse. The device will be inserted through the vagina and cervix so that it sits just inside the uterus. Since it is inside your uterus, the device won’t interfere with sex or prevent you from using tampons.

The two small cross pieces at the top of the T will help to hold the device in place so that it doesn’t slip back through the cervix. There are two small threads that hang down from the bottom of the T. These will pass through the cervix. The doctor will show you how to feel for these strings so that you can check the IUD or IUS is still in the right place. You’ll need to do this about once a month.

As long as the device stays in place, an IUD or IUS should be a very reliable, convenient and long-lasting choice for contraception. Both can be left in place for years at a time and they are more than 99% effective at preventing pregnancies. However, the way that they do this is very different.

How the IUD Works

The IUD is also known as the copper coil because it releases small amounts of copper to prevent you from getting pregnant. Copper is a metal that is naturally found in our bodies in small amounts, so it is very safe when used in an IUD. The device gradually releases copper into the uterus where it prevents pregnancy by:

  • Changing the cervical mucus so that it is less hospitable to sperm. It will be harder for sperm to survive and move through the cervix to reach an egg.
  • Changing the womb lining so that it is harder for a fertilised egg to implant there if any sperm does manage to get through.

An IUD will start working as soon as it is put in place. You can actually use the IUD as a form of emergency contraception that will then provide long term protection. Once it is in place, an IUD can keep working for 5-10 years. However, if you want to change contraception or have a baby, the effects will stop as soon as the device is removed.

How the IUS Works

The IUS is a type of hormonal contraception, so it works in a similar way to the mini contraceptive pill. The device gradually releases the hormone progestogen into your womb. Progestogen can prevent you from getting pregnant by:

  • Making the cervical mucus thicker so that it is harder for sperm to pass through and reach the egg.
  • Reducing the chances of a fertilised egg implanting in the uterine wall if any sperm do get through.
  • Stopping you from ovulating (releasing an egg), in some cases.

An IUS can be fitted at any point in your menstrual cycle, but it won’t always protect you right away. If it is fitted during the first week of your cycle (starting from the first day of your period) then you’ll be protected immediately. If it is fitted later in the cycle, it will take a week to start working. You’ll need to use another form of contraception for the first 7 days.

Once it’s in place, the IUS will keep working for 3-5 years. Your fertility will return to normal right way if you decide to have it removed.

Which One Should You Choose?

Both of these devices can provide reliable, long term protection that you don’t need to think about. You won’t need to pause before sex or remember to take a pill every day. However, the different methods that these two devices create some unique advantages that may help you to choose:

  • The IUD always works immediately and you can use it as emergency contraception.
  • Since it doesn’t use hormones, the IUD won’t cause any of the side effects of hormonal contraceptives, such as headaches, mood changes or acne. You could experience these side effects if you choose the IUS.
  • The hormonal IUS can make your periods lighter and shorter, or may even stop them completely so it can be a good choice if you have menstrual problems. Your periods could actually get heavier or longer in the first 3-6 months after having an IUD fitted.

The disadvantages of these two devices are actually very similar, so they aren’t much help in deciding which one is best for you. However, it’s important to be aware of these issues and to consider other types of contraception that might be a better fit, such as the contraceptive implant, injection or pill.

  • The device might not work properly if it moves out of place. You will need to check the strings regularly and see your doctor if you can’t find them.
  • They can’t protect against STIs, so you should consider using condoms too.
  • There is a small chance that you could develop an infection after getting an IUD or IUS fitted.
  • In rare cases, an IUD or IUS can damage the womb when it is put in. If you experience any pain after having the device fitted, you should see your doctor.
  • If your contraception fails then there is a slightly higher risk of ectopic pregnancy when you’re using an IUD or IUS.

Most women will be able to use either option safely, so it really comes down to personal preferences. The IUD can be the best choice if you want to avoid using hormonal contraception, while the IUS may be better if you have long, painful or heavy periods.

Which one do you think is better?

077 0832 3025