There are three conditions which must be met in order to rely on exclusive breastfeeding as a contraceptive method. The baby must be under six months, you must be exclusively and regularly breastfeeding (including at night), and your period must not have resumed. As long as these three conditions are met, research indicates that there is less than a 1% chance of getting pregnant. Using spermicide in addition further reduces the risk of pregnancy.
If you do not meet all of the above criteria, then the chances of getting pregnant are higher. Spermicide alone in a non breastfeeding woman is 75-85% effective. Exclusive breastfeeding does reduce fertility even with an older infant, so the percentages are likely to be higher.
With any method there is always a risk of getting pregnant. If there are medical contraindications to pregnancy at this point, or if you would be devastated by a pregnancy now, it may be worthwhile to look into progesterone-only pills or the diaphragm in combination with breastfeeding.
You can read our article on choosing a contraceptive method and discuss your available options with your physician.
Please feel free to get back to us with any further questions.