When does depot medroxyprogesterone acetate (DMPA) become effective after injection in a woman who is two months postpartum, still amenorrheic, and partially breastfeeding?

DMPA Effectiveness After Injection at 2 Months Postpartum with Partial Breastfeeding

A woman who is 2 months postpartum, amenorrheic, and partially breastfeeding needs to abstain from sexual intercourse or use backup contraception for 7 days after receiving DMPA injection, as she does not meet the criteria for immediate effectiveness (which requires full or nearly full breastfeeding with ≥85% of feeds being breastfeeds). 1

Key Determination: Breastfeeding Status

The critical factor determining whether backup contraception is needed depends on the intensity of breastfeeding:

• Full or nearly full breastfeeding (≥85% of feeds are breastfeeds): No backup contraception needed if <6 months postpartum and amenorrheic 1
• Partial breastfeeding (<85% of feeds): Requires 7 days of backup contraception 1

Since this patient is partially breastfeeding, she does not qualify for the lactational amenorrhea method (LAM) protection and therefore needs backup contraception.

Timing of Contraceptive Effectiveness

Immediate Effectiveness (No Backup Needed)

DMPA provides immediate contraceptive protection without backup only when: 1

• Started within first 7 days of menstrual bleeding, OR
• Woman is <6 months postpartum, amenorrheic, AND fully/nearly fully breastfeeding (≥85% of feeds)

Delayed Effectiveness (7 Days Backup Required)

For all other scenarios, including this patient's situation: 1

• Woman is ≥21 days postpartum
• Has not experienced return of menstrual cycles
• Does NOT meet full/nearly full breastfeeding criteria
• Must abstain from intercourse or use additional contraception for 7 days

Mechanism Supporting 7-Day Window

The 7-day backup recommendation is based on evidence showing: 1

• DMPA injections given within day 7 of the menstrual cycle reliably inhibit ovulation
• When given after day 7, ovulation may occur in some women initially
• Cervical mucus becomes poor quality (unfavorable for sperm penetration) in 90% of women within 24 hours of injection, providing partial protection 1

However, this partial protection from cervical mucus changes alone is not considered sufficient to eliminate the need for backup contraception in the first 7 days. 1

Pharmacokinetic Support

MPA is detectable in serum within 30 minutes after injection, with levels plateauing at approximately 1.0 ng/mL for about three months, providing sustained ovulation suppression. 2 Despite this rapid absorption, the 7-day backup period accounts for variability in immediate ovulation suppression among individual women. 1

Common Pitfall to Avoid

Do not assume that amenorrhea alone provides contraceptive protection in the postpartum period with partial breastfeeding. The CDC guidelines are explicit that the LAM criteria require full or nearly full breastfeeding (≥85% of feeds), and partial breastfeeding does not provide the same hormonal suppression of ovulation. 1 Return of fertility can occur before return of menses, making backup contraception essential for the first 7 days after DMPA injection in this scenario.

Practical Implementation

For this specific patient: 1

• Administer DMPA injection at 2 months postpartum (safe timing, U.S. MEC 1 at ≥1 month postpartum)
• Confirm reasonable certainty she is not pregnant before injection
• Instruct patient to abstain from intercourse or use barrier contraception for 7 days after injection
• After 7 days, DMPA provides highly effective contraception (failure rate <1% with perfect use)
• Schedule repeat injection in 12 weeks (with 2-week grace period per U.S. recommendations) 1