Three and a half weeks after passing the gestational sac I have period‑like bleeding, a serum β‑human chorionic gonadotropin level of 6 IU/L, an endometrial thickness of 8 mm on transvaginal ultrasound with no intrauterine tissue; could this represent an undetected retained product of conception?

No, You Do Not Have Retained Products of Conception (RPOC)

Your clinical picture—period-like bleeding 3.5 weeks after passing the gestational sac, serum β-hCG of 6 mIU/mL, endometrial thickness of 8 mm, negative urine pregnancy test, and clear ultrasound scans—represents a completed miscarriage that is resolving spontaneously, and no surgical or medical intervention is required. 1

Why RPOC Is Effectively Ruled Out

β-hCG Level Excludes RPOC

• A serum β-hCG of 6 mIU/mL (essentially at the detection limit) combined with an empty uterine cavity on ultrasound effectively rules out retained products of conception 1
• RPOC requires persistent placental or trophoblastic tissue, which would maintain elevated β-hCG levels well above baseline 2
• The Society of Radiologists in Ultrasound defines completed early pregnancy loss as an empty uterine cavity following expulsion of the gestational sac 1

Endometrial Thickness Is Normal

• An 8 mm endometrial thickness after miscarriage falls within the normal post-miscarriage range and does not suggest retained tissue 1
• The guideline threshold for concern regarding RPOC is an endometrial thickness ≥14 mm with vascularity on Doppler ultrasound 1
• Your 8 mm measurement corresponds to a proliferative or early secretory endometrial pattern, which is expected as estrogen and progesterone levels normalize after completed miscarriage 1

Ultrasound Findings Confirm Complete Expulsion

• Clear ultrasound scans showing no intrauterine tissue, combined with your low β-hCG, definitively exclude RPOC 1
• The most specific ultrasound finding for RPOC is a vascular echogenic mass within the endometrial cavity, which you do not have 3
• While a thickened endometrial echo complex (8-13 mm) can suggest RPOC, this finding is nonspecific and overlaps with normal postpartum appearance—and your scans show no mass 3

Why You're Bleeding Now

Normal Post-Miscarriage Physiology

• The bleeding you're experiencing at 3.5 weeks (approximately 25-28 days) after sac expulsion represents normal hormonal withdrawal bleeding as your body transitions back to regular menstrual cycles 1
• This transient shedding occurs as estrogen and progesterone levels normalize following the completed miscarriage 1
• Your negative urine pregnancy test confirms that β-hCG has fallen below the detection threshold (typically 20-25 mIU/mL), which is consistent with complete resolution 4

Expected Timeline

• After a completed first-trimester miscarriage, it typically takes 4-6 weeks for menstrual cycles to resume 1
• Your bleeding at 3.5 weeks likely represents either the tail end of post-miscarriage spotting or the onset of your first post-miscarriage period 1

What You Should Do Next

No Intervention Required

• No surgical evacuation (D&C) is needed because your β-hCG is near zero and ultrasound shows no retained tissue 1
• No medical management (misoprostol) is indicated because the miscarriage has already completed spontaneously 1
• No further β-hCG monitoring is necessary once levels fall below 5 mIU/mL, as yours have 1

Contraceptive Counseling

• Ovulation can resume within 2-4 weeks after a completed miscarriage, so if you wish to avoid pregnancy, initiate contraception immediately 1
• Combined hormonal contraceptives or implants can be started right away without waiting for your next menses 1
• If you start contraception within 7 days of the completed miscarriage, no backup method is needed 1

When to Seek Care

• Return for evaluation if you develop heavy bleeding (soaking more than one pad per hour for 2+ hours), severe abdominal pain, fever >38°C (100.4°F), or foul-smelling vaginal discharge, as these could indicate infection or other complications 1
• Otherwise, expect the bleeding to taper over the next 1-2 weeks as your cycle normalizes 1

Common Pitfalls to Avoid

Don't Confuse Normal Findings with RPOC

• An 8 mm endometrium is not diagnostic of RPOC—the threshold is ≥14 mm with vascularity 1
• Gray-scale ultrasound findings of a thickened endometrium alone are inadequate for diagnosing RPOC; Doppler detection of vascularity is required to increase diagnostic accuracy 2
• Your clear scans showing no mass and no vascularity definitively exclude RPOC 1

Don't Undergo Unnecessary Procedures

• Performing dilation and curettage when β-hCG is near zero and ultrasound is clear risks complications (perforation, infection, Asherman syndrome) without benefit 1
• Expectant management has higher maternal morbidity (60.2% vs. 33.0% with intervention) only when RPOC is actually present—which it is not in your case 1