After a recent miscarriage with passage of tissue, a quantitative β‑hCG of 6 IU/L and an endometrial thickness of 8 mm, I am now bleeding—Is this a normal menstrual period or retained products of conception?

Is This Bleeding a Normal Period or Retained Products of Conception (RPOC)?

With an hCG of 6 IU/L and endometrial thickness of 8 mm following documented passage of the gestational sac, this bleeding is most likely your first normal menstrual period, not RPOC.

Understanding Your Clinical Picture

Your timeline and laboratory values strongly favor a completed early pregnancy loss with return of normal menstruation:

• An hCG level of 6 IU/L is essentially at the threshold of detection and indicates near-complete resolution of pregnancy tissue, as hCG should decline to <5 mIU/mL after complete miscarriage 1
• The endometrial thickness of 8 mm falls below the threshold that raises concern for RPOC, as studies show endometrial thickness alone does not reliably predict retained tissue, and thickness >8 mm was used as a criterion for surgical evaluation but had poor specificity 2
• You documented passage of the gestational sac, which is the critical event in completing a miscarriage 3

Why This Is Likely a Normal Period

The timing and pattern fit expected physiology after miscarriage:

• First menses typically returns 4-6 weeks after pregnancy loss once hCG normalizes 1
• Your hCG has declined appropriately from the time of sac passage to near-zero levels, following the expected quadratic decline pattern where hCG falls 60-84% by day 7 depending on starting concentration 1
• Spotting between the initial bleeding and this current bleeding is common as the endometrium regenerates and hCG continues to decline 3

What RPOC Would Look Like (And Why You Don't Have It)

RPOC has specific diagnostic features that are absent in your case:

• The ultrasound finding of hyperechoic (bright) material within the uterine cavity is the best predictor of RPOC, with 78% sensitivity and 100% specificity 2
• Your endometrial thickness of 8 mm is at the lower threshold; RPOC typically presents with thickened endometrium containing echogenic tissue with vascularity on color Doppler 3, 2
• Persistent or heavy vaginal bleeding is the most common symptom of RPOC (sensitivity 93%), not the on-and-off spotting followed by period-like bleeding you describe 2
• hCG levels plateau or decline slowly with RPOC, whereas your hCG has appropriately declined to 6 IU/L 1

The Diagnostic Algorithm You've Already Completed

Your clinical course has followed the expected pattern for completed miscarriage:

• Initial bleeding and passage of gestational sac = expulsion of pregnancy tissue 3
• Intermittent spotting = normal endometrial shedding as hCG declines 3
• hCG decline to 6 IU/L = confirms near-complete resolution of trophoblastic tissue 1
• Endometrial thickness 8 mm without hyperechoic material = regenerating endometrium, not retained tissue 2
• Return of bleeding resembling a period = first menses after pregnancy loss 3

When to Worry About RPOC

You should seek evaluation if you develop:

• Heavy bleeding soaking through more than 2 pads per hour for 2+ hours 3
• Severe lower abdominal pain (though mild cramping with menses is normal) 2
• Fever or foul-smelling discharge suggesting infection 3
• Persistent bleeding beyond 2 weeks that doesn't follow a normal menstrual pattern 2

Important Caveats

• The term "retained products of conception" (RPOC) is increasingly being replaced with "residual products of conception" to avoid implying that tissue is fixed and requires intervention, when most cases resolve spontaneously 3
• Enhanced myometrial vascularity (increased blood flow in the uterine wall) is a normal, transient finding after miscarriage and should not be confused with RPOC or arteriovenous malformation 3
• If bleeding becomes concerning or hCG fails to reach zero, repeat ultrasound looking specifically for hyperechoic intracavitary tissue with vascularity would be the next diagnostic step 2

Your clinical picture—documented sac passage, hCG of 6 IU/L, endometrial thickness of 8 mm, and return of bleeding after a spotting-free interval—is consistent with completed early pregnancy loss and return of normal menses, not RPOC.