It is possible, though unlikely, to become pregnant during the first month of the Depo-Provera shot, explains Planned Parenthood. Depo-Provera must be given at a specific time based on personal health conditions. If the shot is not taken on schedule, risk of pregnancy increases.
Depo-Provera protects against pregnancy immediately if taken within seven days of starting a period, within five days of miscarriage or abortion or within three weeks after giving birth. If the shot is not taken at the appropriate time, Planned Parenthood strongly suggests using a secondary birth control method for the first week after the shot. Depo-Provera is 99 percent effective with perfect use and 94 percent effective with typical use.