How Does Contraception Work?

Contraception, or birth control, helps prevent pregnancy and there are a variety of different contraceptive methods available. Depending on what you choose, contraception may prevent the sperm from fertilising the ovum, prevent ovulation, or change the endometrium so the fertilised ovum can’t implant.

Personal attitudes towards contraception vary. Some women may decide not to use contraception for cultural, religious, or lifestyle reasons. Many women want to plan when they have children and the number of children they would like to have. Therefore, family planning and contraception go hand in hand.

Methods of Contraception

Contraceptive ChoicesCombined oral contraceptive pillProgestogen only pill IUDDMPA - Depo Provera, Depo RaloveraCondomsMale sterilisationFemale sterilisationImplanon®DiaphragmVaginal ringNatural MethodsEmergency Contraception


How the different methods work:

  • stopping the release of eggs (oral contraceptive pills, hormone injection, vaginal ring)
  • stopping sperm getting into the male ejaculate (vasectomy)
  • stopping the egg and sperm meeting by:
    • using a barrier (condom)
    • thickening the mucus at the cervix to stop the sperm getting through
    • blocking the tubes between the ovary where the eggs are produced and the uterus (female sterilisation)
    • being toxic to the eggs and sperm (copper IUD)
  • making the lining of the womb too thin for the fertilised egg to embed

Overview of methods

The different methods of contraception can be described in different ways.

How long do contraceptives last?

This can range from a permanent method, a long-acting method (three, five or ten years), a medium acting method (four to twelve weeks) or a short acting method (daily).

How are they used?

Contraceptives include:

  • a pill taken by mouth
    an injection or implant under the skin
    an intrauterine device that is inserted into the uterus
    a hormone vaginal ring or a diaphragm that the woman inserts into the vagina
    a condom that covers the male penis or the inside of the vaginal walls

Some women feel more in control by taking a pill each day, while other women prefer a method that they can forget about for most of the time.

How good are they at preventing a pregnancy?

There are a number of safe and effective methods of contraception available in Australia and it is important to find the method that is best for you. Learning about each method may help you make your decision. Only you can decide what is best for you.

There is no method that is 100 per cent effective. The effectiveness of different methods can be measured by ‘perfect-use’ where rules of the method are rigorously followed, and (if applicable) the method is used at every act of intercourse. The failure rates in practice (typical use) are higher than perfect-use rates for a variety of reasons. A person might:

  • be given the incorrect instructions about the how to use the method (eg. starting the pill at the wrong time)
  • make mistakes when using the method (eg. not use a condom properly)
  • forget the requirements for using the method (eg. being late for a contraceptive injection)

For more information, see the Family Planning Alliance Australia Efficacy of contraception methods fact sheet.

’Typical use’ is the rate that should be considered when comparing methods.

Efficacy (Perfect Use/Typical Use)

Combined oral contraceptive pill (99.5% / 93%)  Male condom (98% / 88%) 
Copper IUD (99.5%) Male sterilisation (99.5%)
DMPA - Depo Provera, Depo Ralovera (99.8% / 96%) Mirena® (99.9%)
Female condom (95% / 79%) Progestogen only pill (99.5% / 93%)
Female sterilisation (99.5% / 99.5%) Vaginal ring (99.5% / 93%)
Implanon (99.95% / 99.95%)  

Reference: Trussell J. Contraceptive failure in the United States. Contraception 2011; 83(5):397-404.


Some methods have a regular cost and some an ‘upfront’ cost when it is first used and then a low cost after this. It is wise to compare the methods by looking at the cost over time. The cost needs to be weighed against how effective it is. If a method is not very effective there is a much greater risk of pregnancy which will cost a lot more! For method-specific costs, refer to the 2014 Choice magazine Contraceptive buying guide.

Menstrual bleeding with contraception

  • Some methods do not affect your normal cycle at all (condoms, fertility awareness, diaphragm)
  • All contraceptive methods that contain a hormone will affect your normal cycle
  • The bleeding that occurs with hormones is not a true period (ie. not under the control of your natural hormones)
  • Bleeding when taking hormones is called a withdrawal bleed when it happens regularly (such as on the oral contraceptive pill)
  • Irregular bleeding with hormones is called break-through bleeding (this suggests that the hormones are not controlling the bleeding pattern)
  • You may choose a particular method because the bleeding pattern may suit you and your lifestyle
  • Some methods are particularly recommended for women with heavy periods as they can reduce the bleeding (Mirena IUD)


Emergency Contraception

Emergency contraception can be used as a backup and is not intended as a primary contraceptive method. All people in a new relationship should use condoms to prevent STIs and also be advised about emergency contraception.

Emergency contraception pills can be used up to 96 hours after unprotected sex and can be obtained without a prescription at pharmacies. The copper IUD can also be used as emergency contraception and can be used up to 120 hours after unprotected sex. An IUD needs to be inserted by a doctor.

It is essential to have a follow-up check after 3 weeks to exclude a pregnancy and arrange ongoing contraception.

This method is used when:

  • no contraception was used during sex
  • a women has forgotten to take her contraceptive pills
  • a condom slipped off or broke during sex
  • a female has been sexually assaulted

Around menopause

Any contraception containing oestrogen is not recommended as health risks outweigh the benefits. The levonorgestrel-releasing IUD (Mirena) can be used for contraception, to control heavy menstrual bleeding and to balance the low dose oestrogen used in hormone replacement therapy (HRT).

After a miscarriage or termination of pregnancy

Following a miscarriage or termination, your normal menstrual cycle can resume almost immediately, meaning that it is possible for you to become pregnant again within a few weeks. If you don’t want to get pregnant straight away you will need to think about your contraceptive options.

When choosing contraception, some of the factors that you need to think about are your age, lifestyle, finances, previous contraception and what you think is suitable and acceptable for you. There are many contraceptive options available other than the pill or condoms, and some may be more appropriate to your individual needs than others.

After childbirth

After childbirth you will need to choose an effective contraceptive method if you don’t want to get pregnant straight away. The method of contraception you use depends on what you and your partner prefer, your medical history, any problems you had in your pregnancy and if you are breastfeeding. If a woman is breastfeeding contraceptive methods that contain oestrogen are not recommended.

It is usually advised that you wait until the baby is six months old before you start using contraception that contains oestrogen. This is because oestrogen may reduce your milk flow. However, you can consider using them when your baby is at least six weeks old and at least half bottle fed.

Breastfeeding is 98% effective in preventing pregnancy, but only if:

  • you haven't had a period since your baby was born
  • your baby is less than six months old
  • your baby is only breastfed and not having any other food or drink

This protection reduces significantly after six months and once periods return or the baby starts to have any other food or drink, you will need to use contraception if you don't want to get pregnant.

The following types of contraception are considered safe when breast feeding: the progestogen only pill, condoms, the diaphragm, injection, implant, intrauterine devices and emergency contraception.

There are many myths about when and what contraceptives can and cannot be used after a pregnancy. Most contraceptive methods can be started immediately. If you choose an contraceptive implant, it can be inserted on the same day as the delivery or before you leave the hospital. An IUD can be inserted at the 6-wek check-up or any time after that provided a pregnancy is excluded.

Can I miss periods on the pill?

Some women choose to skip their period by not taking the break between the last hormone pill, and the first hormone pill of the new packet (skipping the sugar pills). It is safe to do this. Talk to your doctor, nurse or other healthcare provider, or ring the True clinic.

Do I need to stop the pill at 35 years?

Most women can use the contraceptive pill up to the age of 50 years. However, there are increased risks for women over 35 years and smoking would be a contraindication to continue the pill after this time. A discussion with your doctor about contraception after 35 years age is advised.

How soon will my fertility return after an IUD?

An IUD may last for five to ten years (depending on the type) but can be removed at any time. After removal your fertility will return within a month.

Can I have an IUD as emergency contraception?

Yes, the copper IUD can be used as emergency contraception if inserted up to five days after unprotected sexual course. This is more effective than the emergency contraceptive pill (the “morning after pill”). It also provides ongoing contraception. The Mirena™ cannot be used as emergency contraception.

Can I use an IUD after I have had a baby?

Yes, you can use an IUD after having had a baby. This can be fitted from six weeks after the birth, regardless of whether you have had a vaginal or caesarean delivery. IUDs are safe for breastfeeding women to use. It will be important to check that you are not pregnant before the IUD is fitted.

Can I use an IUD for heavy periods?

The Mirena™ releases a low dose of the hormone progestin. The Mirena™ was originally developed to treat heavy periods in addition to providing contraception. The Mirena™ can be a good choice for women, as it can decrease heavy periods. Heavy bleeding can be due to hormones or other gynaecological problems. Before you have an IUD inserted it is important to be sure you have none of these gynaecological problems. Your doctor will arrange a check-up and may want to arrange other tests before you have a Mirena.

What is the best contraception to prevent a sexually transmitted infection (STI)?

The condom is the only method of contraception that helps prevent STIs. Using a condom before genital contact offers protection against many STIs.

What is the best contraception to prevent a pregnancy?

The contraceptive method that has the same efficacy for perfect use and typical use is long acting reversible contraceptives (LARC). The best LARCs are the intrauterine devices (IUDs) and the progestogen implant (Implanon).

Considerations when choosing contraception, available in 6 languages

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