How long after a sexual encounter can a pregnancy test yield a positive result?

Timing of Positive Pregnancy Test After Sexual Intercourse

A urine pregnancy test can first detect pregnancy approximately 9-11 days after sexual intercourse that results in conception, with 98% of tests becoming positive by the time of the expected period (approximately 14 days post-conception). 1

Understanding the Timeline from Intercourse to Positive Test

The Fertile Window and Conception

• Conception can only occur during a 6-day window ending on the day of ovulation, with the highest probability (33%) when intercourse occurs on ovulation day itself. 2
• Intercourse occurring 5 days before ovulation has approximately a 10% chance of resulting in conception. 2
• In a typical 28-day cycle, ovulation generally occurs between days 9-20, though this varies considerably between women. 3

Implantation and hCG Production

• Human chorionic gonadotropin (hCG) first appears in maternal blood 6-8 days after fertilization (which corresponds to 6-8 days after the sexual encounter that resulted in conception). 1
• The fertilized egg must implant in the uterine lining before hCG production begins, which typically occurs 6-12 days after fertilization. 4

When Tests Become Positive

Earliest Detection

• With current pregnancy test sensitivity (25 mIU/L), urine tests may show positive results 3-4 days after implantation. 1
• This translates to approximately 9-12 days after the sexual encounter that resulted in conception (6-8 days for implantation plus 3-4 days for detectable hCG levels). 1

Reliable Detection Timeline

• By 7 days after the missed period (approximately 21 days post-conception), 98% of pregnancy tests will be positive. 1
• Most FDA-approved qualitative urine pregnancy tests have a sensitivity of 20-25 mIU/mL, which is sufficient to detect most pregnancies by the time of a missed period. 3

Important Limitation

• Pregnancy tests cannot detect a pregnancy resulting from recent sexual intercourse - there must be adequate time for fertilization, implantation, and hCG production. 3

Practical Clinical Guidance

Testing Recommendations

• For women with regular 28-day cycles: Test on the first day of the missed period (approximately 14 days after ovulation/sexual encounter) for reliable results. 1
• If testing earlier: A negative result does not rule out pregnancy, as hCG levels may not yet be detectable. 3
• If negative one week after missed period: This virtually guarantees the woman is not pregnant. 1

Key Caveats

• Some studies show that an additional 11 days past the expected menses may be needed to detect 100% of pregnancies using qualitative tests, highlighting variability in test sensitivity and individual hCG production. 3
• Pregnancy detection rates vary due to differences in test sensitivity and timing relative to missed menses. 3
• Women with irregular cycles may have difficulty accurately predicting when to test, as ovulation timing can be highly variable. 5

Clinical Context for Recent Intercourse

• If a woman has had unprotected sexual intercourse within the last 5 days and pregnancy is not desired, emergency contraception should be considered, as pregnancy testing will not yet be informative. 3
• The accuracy of pregnancy tests is limited relative to the time of last sexual intercourse, and providers should be aware of this when counseling patients. 3