Unit Converter
Human chorionic gonadotropin (hCG)
(Placental Glycoprotein Hormone – Pregnancy Marker & Tumor Marker)
Synonyms
- hCG
- Human chorionic gonadotropin
- Beta-hCG
- Total hCG
- Intact hCG
- Free β-hCG
- Tumor marker hCG
Units of Measurement
- mIU/mL
- IU/L
Unit Conversion
1 mIU/mL = 1 IU/L
(Direct equivalence; no further conversion needed.)
Description
hCG is a glycoprotein hormone produced primarily by placental syncytiotrophoblast cells beginning shortly after implantation.
Structure:
- α-subunit (shared with LH, FSH, TSH)
- β-subunit (unique to hCG → diagnostic specificity)
Key physiological roles:
- Maintains corpus luteum → progesterone production
- Supports early pregnancy
- Modulates maternal–fetal immune tolerance
- Stimulates fetal Leydig cells (male sexual differentiation)
Clinically, hCG is a fundamental biomarker for:
- Pregnancy detection
- Ectopic pregnancy evaluation
- Monitoring early pregnancy viability
- Diagnosing trophoblastic tumors
- Tumor marker in germ-cell cancers
Clinical Significance
1. Pregnancy Testing (Primary Use)
hCG appears:
- Detectable in serum: ~10 days after conception
- Detectable in urine: by missed period
Serum tests detect:
- Intact hCG
- Free β-hCG
- hCG variants (hyperglycosylated, nicked, etc.)
Normal early pregnancy pattern
- hCG approximately doubles every 48–72 hours in early gestation
- Peaks at 8–10 weeks
- Slowly declines and plateaus in mid-pregnancy
2. Ectopic Pregnancy
Abnormal rise:
- hCG rises slower than doubling
- Plateauing or falling hCG suggests non-viable or ectopic pregnancy
Used with:
- Transvaginal ultrasound
- Clinical evaluation
3. Monitoring Early Pregnancy Viability
Low or slowly rising hCG may indicate:
- Threatened miscarriage
- Missed abortion
- Ectopic pregnancy
Rapid rise (>100% in 2 days) can be normal or suggest twin gestation.
4. Gestational Trophoblastic Disease (GTD)
hCG often extremely high in:
- Hydatidiform mole (complete/partial molar pregnancy)
- Gestational choriocarcinoma
- Invasive mole
Serial hCG helps monitor:
- Treatment response
- Remission
- Recurrence
5. Tumor Marker in Males & Non-Pregnant Females
hCG produced by some tumors:
- Testicular germ cell tumors
- Seminoma (mild elevation)
- Non-seminomatous germ-cell tumors (very high hCG)
- Ovarian germ-cell tumors
- Hepatocellular carcinoma (rare)
- Lung carcinoma (rare)
Reference Intervals
(Tietz 8E + ACOG + Mayo + ARUP)
Non-Pregnant
- < 5 mIU/mL (5 IU/L) = negative
- 5–25 mIU/mL = equivocal → repeat in 48 hrs
Pregnancy – Typical hCG Ranges
| Gestational Age | hCG (mIU/mL) |
| 3 weeks | 5 – 50 |
| 4 weeks | 5 – 426 |
| 5 weeks | 18 – 7340 |
| 6 weeks | 1080 – 56,500 |
| 7–8 weeks | 7650 – 229,000 |
| 9–12 weeks | 25,700 – 288,000 |
| 2nd trimester | 13,000 – 140,000 |
| 3rd trimester | 10,000 – 60,000 |
Tumor Marker Cutoffs
- >5 mIU/mL in non-pregnant woman → abnormal
- >2 mIU/mL in adult males → abnormal
- >5,000–10,000 mIU/mL = typical for GTD
- >100,000 mIU/mL = strongly suggests molar pregnancy
Diagnostic Uses
1. Detect Pregnancy
Most common clinical application.
2. Assess Pregnancy Viability
Serial measurements (every 48 hours) critical for:
- Early pregnancy failure
- Ectopic pregnancy
- Pregnancy of unknown location (PUL)
3. Monitor Trophoblastic Disease
- Treatment monitoring
- Detecting relapse
- Risk stratification
4. Tumor Marker in Males
Especially for:
- Testicular germ-cell tumors
- Choriocarcinoma
5. Prenatal Screening
Free β-hCG used in:
- First-trimester Down syndrome screening
- Combined aneuploidy screening (PAPP-A + NT + hCG)
Analytical Notes
- Serum hCG more sensitive than urine
- Choose quantitative test when clinical assessment needed
- “Hook effect” possible in very high hCG → false-low
- Different assays detect different hCG isoforms
- Always correlate with ultrasound and clinical findings
Clinical Pearls
- hCG does not need to double exactly - acceptable rise is ≥35% in 48 hours.
- Molar pregnancy often has extremely high hCG (>100,000).
- Post-treatment GTD requires weekly hCG until undetectable, then monthly.
- Elevated hCG in males is almost always pathologic.
- Free β-hCG is elevated in Down syndrome pregnancies.
Interesting Fact
Hyperglycosylated hCG (hCG-H) is the dominant isoform in very early pregnancy and is crucial for trophoblast invasion and placenta formation.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Hormones & Pregnancy Testing.
- ACOG Practice Bulletin - Early Pregnancy Detection & Ectopic Pregnancy.
- FIGO Guidelines - Gestational Trophoblastic Disease.
- Mayo Clinic Laboratories - hCG.
- ARUP Consult - hCG Testing & Tumor Markers.
- MedlinePlus / NIH - hCG Test.