Implantation Bleeding: Frequency, Characteristics & Differentiation from Menses

Implantation bleeding occurs when blastocyst attaches to endometrium (~6–10 days post-ovulation).

Epidemiology

• Reported in 15–25% of clinical pregnancies.
• Often unrecognized (mistaken for early light period).

Characteristics

• Timing: 10–14 DPO (days past ovulation), ~1 week before expected menses.
• Volume: Spotting only (few drops, not filling pad/tampon).
• Color: Pink, brown (old blood), not bright red.
• Duration: Hours to 1–2 days.
• Absence of: Clots, severe cramps, heavy flow.

Differential

• Early miscarriage (chemical pregnancy).
• Cervical irritation (exam, intercourse).
• Breakthrough bleeding (OCP).
• Ectopic pregnancy (pain + bleeding = emergency).

Confirm with quantitative hCG (doubling q48h) and ultrasound at 5.5–6 wks. Absence of implantation bleeding does not exclude pregnancy.