Not likely if all conditions are meant. They are 90-95% chances of not getting pregnant. Once you stop having the 3-monthly contraceptive injection, it can take up to a year for you to return to fertility and be able to get pregnant2. However, in most women, the effect will have worn off 5 to 6 months after the last injection. Over 80 % of women will conceive within a year of their last injection.