Pregnancy Risk with Day 2 Intercourse and Day 4 Levonorgestrel
Yes, pregnancy is possible but unlikely in this scenario, as levonorgestrel taken on day 4 (48 hours post-intercourse) should provide effective protection since intercourse occurred during menstruation when fertility is extremely low and the medication was administered well within the optimal 72-hour window.
Understanding the Timing and Mechanism
The critical factor here is that intercourse on day 2 of menstruation occurs far outside the fertile window, which typically spans days -5 to 0 relative to ovulation (usually around day 14 in a 28-day cycle). 1, 2
How Levonorgestrel Works
- Levonorgestrel prevents pregnancy primarily by delaying or preventing ovulation, not by affecting implantation. 1, 3, 2
- The medication is highly effective when taken before ovulation occurs, with studies showing zero observed pregnancies when taken on days -5 to -2 before ovulation (compared to 4 expected pregnancies). 1
- When taken after ovulation has already occurred, levonorgestrel shows no protective effect, with observed pregnancies matching expected rates. 1, 2
Efficacy Within 72 Hours
- Levonorgestrel should be taken as soon as possible within 72 hours (3 days) of unprotected intercourse for maximum effectiveness. 4, 5
- Taking the medication on day 4 (48 hours post-intercourse) falls well within this window and maintains good efficacy. 4, 6
- Pregnancy rates remain low when administered within the first 4 days after intercourse, but increase significantly on day 5, with odds ratios for pregnancy on day 5 being almost 6 times higher than day 1. 6
Why This Scenario Is Low Risk
The combination of two protective factors makes pregnancy highly unlikely:
Menstrual timing: Day 2 of the menstrual cycle is during active bleeding, when the endometrium is shedding and no mature follicle exists. Ovulation typically doesn't occur until approximately day 14 in a standard cycle. 1, 2
Timely levonorgestrel administration: The 48-hour delay (day 4 administration) is within the highly effective window, and since ovulation is still approximately 10 days away, the medication will successfully delay or prevent ovulation. 4, 1, 6
Critical Follow-Up Actions
After taking levonorgestrel, the following steps are essential:
Expect the next period at the expected time or within one week of the expected time. If the period is delayed by more than one week, pregnancy testing is necessary. 5
Use barrier contraception or abstain from intercourse for 7 days after taking levonorgestrel if starting or resuming regular hormonal contraception. 4
Obtain a pregnancy test if withdrawal bleeding does not occur within 3 weeks of taking the emergency contraceptive. 4
Important Caveats
Common pitfalls to avoid:
Do not rely on levonorgestrel as regular contraception—it is less effective than standard contraceptive methods and is intended only for emergency use. 5
Be aware that levonorgestrel may be less effective in obese women (>165 pounds), though this is less relevant in this specific scenario given the timing during menstruation. 7
Severe abdominal pain after taking levonorgestrel requires immediate medical attention to rule out ectopic pregnancy. 5