A patient who has been using depot medroxyprogesterone acetate (DMPA) injection, is 11 weeks and 3 days since her last injection, meets UKMEC criteria for combined hormonal contraception (CHC), and wishes to start a combined transdermal contraceptive patch today; how many days will it take for the patch to become effective?

The combined transdermal patch will be effective after 7 consecutive days of use

Since the patient is 11 weeks and 3 days (approximately 80 days) since her last DMPA injection—which is more than 2 weeks late (≥15 weeks would be the next scheduled injection at 13 weeks)—she should be treated as a "new start" when initiating the combined hormonal contraceptive (CHC) patch, requiring 7 consecutive days of backup contraception. 1

Clinical Reasoning

DMPA Coverage Status

The patient's last DMPA injection was at 11 weeks and 3 days ago. According to CDC guidelines:

• DMPA is administered every 13 weeks (3 months) 2
• If <2 weeks late (<15 weeks after previous injection): proceed with injection, no backup needed
• If ≥2 weeks late (≥15 weeks): treat as new start, requiring 7 consecutive days of backup contraception 1

At 11 weeks and 3 days, the patient is still within the 13-week window but approaching the end of reliable contraceptive coverage. While technically not "late" yet, she is beyond the optimal reinjection timeframe.

Switching to CHC Patch Protocol

When switching from another contraceptive method to a CHC (including the transdermal patch):

Timing considerations:

• CHC can be started immediately if reasonably certain the patient is not pregnant 3, 4
• No need to wait for next menstrual period 3

Backup contraception requirements:

• If started >5 days since menstrual bleeding started: abstain from intercourse or use barrier methods for 7 consecutive days 3, 4
• Since this patient is amenorrheic on DMPA (no regular bleeding), she falls into the amenorrhea category requiring 7 days of backup 3

Evidence Strength

The 2013 and 2015 CDC U.S. Selected Practice Recommendations 1, 3 and the updated 2024 guidelines 4 consistently recommend 7 days of backup contraception when:

1. Starting CHC in amenorrheic patients
2. Starting CHC >5 days after menses
3. Switching from DMPA when timing is uncertain

Important Clinical Caveats

Pregnancy exclusion is critical: Before starting the patch, ensure reasonable certainty that the patient is not pregnant. Given she's on DMPA with no regular bleeding pattern, consider:

• Urine pregnancy test today
• Last unprotected intercourse timing
• Any symptoms suggestive of pregnancy

Emergency contraception consideration: If the patient had unprotected intercourse in the past 5 days and is concerned about pregnancy risk, emergency contraception should be considered before or concurrent with patch initiation 1

Blood pressure measurement required: Unlike DMPA, CHC initiation requires blood pressure measurement before starting 4

Practical application instructions:

• Apply first patch today
• Use condoms or abstain from intercourse for the next 7 consecutive days
• Keep the same patch-change day throughout use
• Change patch weekly for 3 weeks, followed by 1 patch-free week

Common pitfall: Do not assume DMPA provides ongoing contraceptive coverage beyond 13 weeks. While MPA can be detected in serum for up to 9 months after injection 5, contraceptive efficacy is not guaranteed beyond the 13-week interval, and ovulation can resume when MPA levels fall below 0.1 ng/mL 5.