Depot Injection Timing Calculation
No, your patient is not too early—she is actually right on time or potentially slightly late, depending on which specific date in the month she received her injection. Depot medroxyprogesterone acetate (DMPA/Depo-Provera) is administered every 12 weeks (3 months), with a 2-week grace period allowing injections from 10-14 weeks after the previous dose without requiring backup contraception 1.
How to Calculate the Reinjection Window
The standard DMPA dosing schedule works as follows:
- Standard interval: Every 12 weeks (84 days)
- Early window: Can be given as early as 10 weeks (70 days) after last injection
- Late window: Up to 14 weeks (98 days) is considered on-time
- Grace period: The full acceptable range is 10-14 weeks 1
Your Patient's Timeline
Without the exact dates, if she received her injection approximately 3 months ago and is presenting now, she falls within the standard reinjection timeframe. The 2-week grace period means she can receive her injection anywhere from 2 weeks before to 2 weeks after the 12-week mark.
Clinical Action Based on Timing
If she is < 2 weeks late (< 15 weeks after previous injection):
- Proceed with injection immediately
- No backup contraception needed
- No pregnancy test required if she has been consistently using the method 1
If she is ≥ 2 weeks late (≥ 15 weeks after previous injection):
- Treat as a new start
- Require 7 consecutive days of backup contraception
- Consider emergency contraception if recent unprotected intercourse 1
Common Pitfall to Avoid
Many clinicians mistakenly believe patients must return exactly at 12 weeks. This rigid interpretation leads to unnecessary visits and missed opportunities for timely reinjection. The evidence shows pregnancy rates during the 2-week grace period (10-14 weeks) are zero or very low 2. Research on return to ovulation after DMPA demonstrates that the earliest ovulation typically does not occur until 15-49 weeks after the last injection, providing substantial protection even beyond the labeled interval 2.
Bottom line: Administer the injection today if she is within 14 weeks of her last dose. She is not early—she is appropriately timed for her reinjection.