Norethisterone + Estradiol Injection on Last Day of Menstruation
Yes, a patient can receive norethisterone + estradiol injection on the last day of menstruation, but backup contraception for 7 days is required because this timing falls outside the optimal 5-day window from the start of menses. 1
Timing Guidelines for Combined Hormonal Contraceptives
The CDC provides clear guidance on when combined hormonal contraceptives (including estradiol/norethisterone combinations) can be initiated:
- Within first 5 days of menstrual bleeding: No backup contraception needed 1
- After day 5 of menstrual bleeding: Requires 7 days of backup contraception (abstinence or barrier method) 1
The "last day of menstruation" typically falls beyond day 5 for most women, placing this scenario in the second category requiring backup protection.
Backup Contraception Requirements
When initiating combined hormonal contraceptives after day 5 of menses, the patient must:
- Abstain from sexual intercourse OR use additional contraceptive protection (condoms) for the next 7 consecutive days 1
- This 7-day interval reflects the time needed to reliably suppress ovulation with combined hormonal methods 1
Pregnancy Exclusion
Before administering the injection, ensure reasonable certainty that the patient is not pregnant 1. The CDC's pregnancy checklist can guide this assessment, though being on the last day of menstruation provides some reassurance.
Clinical Rationale
Combined hormonal contraceptives started after day 5 may not reliably inhibit ovulation immediately in all women 2. The 7-day backup period accounts for:
- Variable ovulation suppression timing across individuals 2
- Potential for residual follicular development from the current cycle 1
- Time needed for cervical mucus changes and endometrial effects to provide full contraceptive protection 1
Common Pitfall to Avoid
Do not delay the injection unnecessarily by requiring the patient to wait for her next menstrual period. The CDC explicitly states that "waiting for her next menstrual period is unnecessary" when initiating combined hormonal contraceptives 1. Starting immediately with appropriate backup contraception is preferable to creating a gap in contraceptive coverage that could result in unintended pregnancy.
Practical Implementation
- Administer the norethisterone + estradiol injection on the last day of menstruation 1
- Counsel the patient to use condoms or abstain from intercourse for 7 days following injection 1
- Document the timing relative to menstrual cycle and backup contraception counseling 1
- Schedule follow-up according to the specific formulation's dosing interval 3