If you breastfeed, you may find that your menstrual cycle takes a while to resume after birth – sometimes up to a year or more, and this can lead to some confusion about whether you are actually ovulating and can get pregnant.

So, this year for World Breastfeeding Week (1 to 8 August) we are looking at fertility after giving birth and the effects breastfeeding has on ovulation.

It has often been considered an old wives’ tale, but in fact, there is some truth to breastfeeding preventing pregnancy in the immediate months following birth. Lactational amenorrhoea is the term used to describe the pause in menstruating while fully breastfeeding, and is essentially nature’s way of preventing pregnancy soon after birth to give your body a chance to heal.

If lactational amenorrhoea is used perfectly the failure rate is less than 2%, making it a very effective post-birth contraceptive method. It is important to note that the effectiveness does depend on certain conditions, so before you decide to rely on breastfeeding as your only contraceptive method, it is important to know why and how it works.

When a parent is exclusively breastfeeding their baby, the body produces high levels of an ovulation-suppressing hormone called prolactin. Studies have found that it seems to be specifically when the nipple is stimulated from the baby suckling that levels of prolactin in the blood increase. If the baby is exclusively breastfed, and at regular intervals (at least every 6 hours during the night and every 4 hours during the day), prolactin levels in the blood remain elevated for the first months following birth.

As long as prolactin levels are high, it is highly unlikely you will ovulate and therefore for your periods to come back, at least in the first six months following birth.

Prolactin levels can quickly decrease however if supplementary formula is introduced, and when baby starts on solid foods, as this reduces the frequency of breastfeeds. Prolactin levels also naturally decrease over time, which is why this method is only considered reliable for the first six months following birth. It only takes about seven days from when breastfeeding ceases for prolactin levels to go back to what they were pre-pregnancy.

If you do get your period (at least two consecutive days of bleeding any time from about 6 – 8 weeks after giving birth) even if you are fully breastfeeding, you are at risk of getting pregnant.

Interestingly, studies have shown that expressing milk may not be as effective at stimulating the production of prolactin, and similarly if the nipples have been numbed with for example an anaesthetic. There are also other factors that can affect prolactin levels such as smoking and depression.

While it is difficult to know exactly when your menstrual cycle will resume, you can be certain that the less you breastfeed the more likely that your cycle will kick back into action. If you choose not to breastfeed at all, you can expect your menstrual cycle to resume within the first few months after birth.

As you can never be quite sure when ovulation will begin after birth, you may want to use other methods of contraception after birth to be on the safe side. If you would like to consider lactational amenorrhoea as a method of contraception, make sure you talk to your doctor or midwife to see if this is the right method for you.