There was a study done on this a few years back which showed that exclusive breastfeeding is around 98% effective as a contraceptive (about the same as the pill) for the first 6 months, but only if all the following conditions are met:

- Baby is exclusively breastfed - no solids, formula or other drinks
- The baby feeds at least once during the night - preferably between 1am and 5am as the hormones are higher when you feed at this time
- Your periods haven't returned.

From 6 months solids etc start to be introduced so the effectiveness drops a lot.

However, if you REALLY don't want to get pregnant, it might be an idea to take extra precautions.

The mini-pill can impact on breastfeeding for some mums so it is a good idea to discuss your options with a doctor or family planning clinic.