Breastfeeding can be used as a contraceptive method known as the Lactation Amenorrhoea Method
Up to 98% effective if the following criteria are adhered to:
Fully breastfeeding regularly (at least every four hours during the day and every 6 hours at night)
Your baby is less than six months old
You have no periods
If any of the above criteria don't apply, the risk of pregnancy increases, and you should consider using another method of contraception if you don’t want to get pregnant.