What do I need to know about the ongoing use of DMPA? Follow up DMPA injections are given every 12 weeks to continue protection against pregnancy. If you go beyond 12 weeks from your last injection you may be at risk of pregnancy. If you aren't certain what to do, seek further advice as soon as possible, particularly if you think you may need Emergency Contraception. To renew your DMPA prescription you will need to see a doctor for review once a year. A review of risks for loss of bone density (osteoporosis) will take place at this visit.