What are the normal Human Chorionic Gonadotropin (HCG) levels based on gestation?

Normal Human Chorionic Gonadotropin (HCG) Levels Based on Gestation

Normal HCG levels vary significantly throughout pregnancy, with a characteristic rise in early pregnancy followed by a plateau and then decline, with specific ranges corresponding to different gestational ages.

Early Pregnancy HCG Levels

• Detection threshold: Intrauterine gestational sac can be detected by transvaginal ultrasound when HCG levels reach approximately 1,000-2,000 mIU/mL 1

• Weeks 3-4 (days 21-28): HCG typically becomes detectable in serum

• Week 5 (days 29-35):

  • Mean HCG level at detection of 1-3mm gestational sac: 730 mIU/mL (range 467-935 mIU/mL) 2
  • By day 32-33, gestational sac should be visible with HCG >1,000 mIU/mL 3

• Week 6 (days 36-42):

  • Yolk sac becomes visible at mean of 36 days with mean HCG of 4,130 mIU/mL (range 1,120-7,280 mIU/mL) 2
  • All normal pregnancies show yolk sac when HCG reaches 7,200 mIU/mL 3

• Week 7 (days 43-49):

  • Fetal cardiac activity visible at mean of 41.1 days with mean HCG of 12,050 mIU/mL (range 5,280-22,950 mIU/mL) 2
  • All viable pregnancies show cardiac activity when HCG exceeds 10,800 mIU/mL 3

Peak and Plateau Phase

• Weeks 8-10: HCG levels peak at approximately 100,000 mIU/L around the ninth week of gestation 4
• Weeks 10-14: HCG levels begin to plateau and then gradually decline

Important Clinical Considerations

Discriminatory Zones

• A transvaginal ultrasound should detect an intrauterine pregnancy when HCG levels exceed 1,500-2,000 mIU/mL 1
• Absence of intrauterine pregnancy with HCG >2,000 mIU/mL increases likelihood of ectopic pregnancy 1
• Safety margin for the discriminatory zone is approximately 750 mIU/mL with transvaginal sonography 5

Abnormal Patterns Requiring Evaluation

• HCG levels that plateau for 4 consecutive values over 3 weeks 6
• HCG levels that rise >10% for 3 values over 2 weeks 6
• HCG persistence for 6 months or more after miscarriage 6
• Markedly elevated HCG levels (>100,000 mIU/mL) in early pregnancy may indicate multiple gestation, molar pregnancy, or rarely hyperreactio luteinalis 4

Post-Miscarriage Monitoring

• After miscarriage, HCG levels should be monitored every 1-2 weeks until normalization 6
• Normalization is defined as 3 consecutive normal assays 6
• Continued monitoring with two measurements at 3-month intervals is recommended to ensure levels remain normal 6

Correlation Between HCG Levels and Ultrasound Findings

Gestational Structure	Mean HCG Level (mIU/mL)	Gestational Age (days)	Sac Size (mm)
Gestational sac	730 (467-935)	31.2 (30-33)	1-3
Yolk sac	4,130 (1,120-7,280)	36.0 (34-38)	>6
Fetal cardiac activity	12,050 (5,280-22,950)	41.1 (39-43)	>9

Caveat

It's important to note that there can be significant variation in normal HCG levels between individuals, and clinical decisions should not be based solely on a single HCG measurement but rather on the pattern of change over time and correlation with ultrasound findings.