At 25 days after passing the gestational sac, with serum human chorionic gonadotropin ~6 mIU/mL, negative urine pregnancy test, endometrial thickness 8 mm and two ultrasounds showing an empty uterus, is my new moderate red bleeding uterine shedding (post‑miscarriage) or a true menstrual period, or could it represent retained products of conception?

Is This New Bleeding a Period or Uterine Shedding?

Your new moderate red bleeding at 25 days post-miscarriage, with HCG of 6 mIU/mL, negative urine pregnancy test, 8 mm endometrial lining, and two clear ultrasounds, most likely represents your first menstrual period returning rather than retained products of conception (RPOC). 1

Why This Is Likely Your Period

HCG and Pregnancy Test Results Point Away from RPOC

• An HCG level of 6 mIU/mL with a negative urine pregnancy test indicates near-complete resolution of trophoblastic tissue, making RPOC extremely unlikely 1
• Serial HCG measurements that decline to undetectable or near-undetectable levels confirm resolution of pregnancy tissue 1
• If RPOC were present, you would typically see persistent or rising HCG levels, not the declining pattern you demonstrate 1

Your Ultrasound Findings Are Reassuring

• Two scans showing a clear uterus with 8 mm endometrial thickness is a normal postpartum finding and represents physiologic healing, not RPOC 1
• An endometrial thickness less than 10 mm has a high negative predictive value for incomplete early pregnancy loss 2
• The most diagnostic ultrasound finding for RPOC is hyperechoic material with internal vascularity on Doppler imaging—which you do not have 2, 3
• The absence of hyperechoic material combined with absence of ongoing bleeding makes RPOC extremely unlikely (negative predictive value 95%) 3

Timeline Supports Return of Menstruation

• First menstruation typically returns 4-6 weeks after early pregnancy loss, and you are at day 25 (approximately 3.5 weeks) 1
• The spotting pattern you describe (brown, red, pink on and off) is consistent with hormonal fluctuation as your cycle re-establishes 1
• This new moderate red bleeding likely represents endometrial shedding as your normal menstrual cycle resumes 1

Why RPOC Is Unlikely in Your Case

Clinical Criteria Not Met

• RPOC typically presents with persistent heavy vaginal bleeding, not intermittent spotting followed by moderate bleeding 4, 1
• You lack the cardinal signs: persistent bleeding requiring >1 pad per hour, fever ≥38°C, foul-smelling discharge, or pelvic pain with uterine tenderness 4, 1
• Vaginal bleeding as the sole symptom without hyperechoic material on ultrasound has only 74% positive predictive value for RPOC 3

Imaging Excludes RPOC

• The combination of no hyperechoic material on ultrasound AND no persistent heavy bleeding gives a 95% negative predictive value for RPOC 3
• Incomplete early pregnancy loss is defined as intracavitary tissue with internal vascularity or a persistent gestational sac—neither of which you have 2
• Your 8 mm endometrial stripe falls well below the threshold; endometrial thickness up to 20-25 mm in the early postpartum period is nonspecific and should not be used alone to diagnose RPOC 1

Important Caveats and When to Seek Care

Avascular RPOC Is Rare But Possible

• Absence of Doppler vascularity does not completely rule out RPOC, as avascular retained tissue can occur in rare cases 1
• However, this is uncommon and would typically be accompanied by other clinical signs 2, 1

Red Flags Requiring Immediate Evaluation

• Heavy vaginal bleeding defined as >1 pad per hour for ≥2 continuous hours 1
• Fever ≥38°C (100.4°F) or foul-smelling discharge 1
• Severe pelvic pain or signs of hemodynamic instability (dizziness, syncope) 1
• If bleeding persists beyond 6 weeks or suddenly increases in volume, re-evaluation is required 1

Follow-Up Monitoring

• Continue to monitor that bleeding follows a normal menstrual pattern (3-7 days of flow, then resolution) 1
• If you have access to repeat HCG testing, a progressive decline to undetectable levels confirms complete resolution 1
• Any plateau or rise in HCG over consecutive measurements would warrant urgent re-evaluation for gestational trophoblastic disease or persistent RPOC 1

Bottom Line

Given your near-zero HCG, negative pregnancy test, normal 8 mm endometrial thickness, two clear ultrasounds, and appropriate timeline, this moderate red bleeding represents your first post-miscarriage menstrual period, not RPOC or pathologic uterine shedding. 1, 3 The intermittent spotting you experienced beforehand reflects normal hormonal fluctuation as your cycle re-establishes. Monitor for the red flags listed above, but expect this bleeding to follow a normal menstrual pattern and resolve within a week.