What are the normal human chorionic gonadotropin (hCG) levels by weeks of gestation in a pregnant individual?

hCG Ranges by Weeks of Pregnancy

A patient is considered pregnant when serum hCG exceeds 5 mIU/mL, but specific weekly ranges are not standardized in clinical guidelines because hCG values vary widely between individuals and the pattern of rise matters more than absolute values. 1

Key Principles for Interpreting hCG Levels

• Pregnancy confirmation occurs at serum hCG >5 mIU/mL, though values ≤5 mIU/mL may occur in healthy nonpregnant patients 1
• Single hCG measurements have limited diagnostic value; serial measurements 48 hours apart provide more meaningful clinical information 2
• hCG doubling time is not constant but increases with advancing gestational age and rising hCG concentrations, ranging from 1.4 to 3.5 days in early pregnancy 3

General Patterns Through First Trimester

Early Detection and Peak Timing

• hCG becomes detectable as early as 6 days after conception using sensitive serum assays 4
• Peak hCG levels occur between 56-68 days (8-10 weeks) of gestation, followed by a decline to a nadir at 18 weeks 4
• No secondary rise occurs in the third trimester; historical reports of late-pregnancy peaks were due to assay cross-reactivity 4

Critical Thresholds for Ultrasound Correlation

The discriminatory hCG threshold of approximately 3,000 mIU/mL is the level at which a gestational sac should be visible on transvaginal ultrasound, though this has limited diagnostic utility for predicting ectopic pregnancy 2

• At hCG 1,000-3,000 mIU/mL: gestational sac typically becomes visible (approximately 5 weeks GA) 2
• At hCG >3,000 mIU/mL: gestational sac, yolk sac, and possibly embryo should be visible 2
• At hCG 6,145 mIU/mL: gestational sac and yolk sac should definitively be present 2

Expected Rise Patterns in Viable Pregnancy

• In viable early intrauterine pregnancy, hCG typically shows 53-66% rise over 48 hours 2
• Doubling times increase as pregnancy advances: the exponential rate of hCG increase significantly decreases with gestational age 3
• Wide fluctuations can occur in early pregnancy, with variations exceeding tenfold during the first trimester, though these decrease with advancing gestation 5

Important Clinical Caveats

Why Specific Weekly Ranges Are Not Provided

Given the multitude of hCG assays available, specific values and terminology vary, and centers are encouraged to refer to local laboratory guidelines 1. The wide individual variation makes absolute ranges unreliable for clinical decision-making 4, 3.

Factors Affecting hCG Interpretation

• Fetal sex influences hCG concentrations: high hCG in late first trimester associates with increased fetal growth in females but not males 6
• Age affects baseline hCG in nonpregnant women: postmenopausal women (>55 years) can have hCG up to 13.1 IU/L without pregnancy 7
• Different assays detect different hCG isoforms: when results don't fit the clinical picture, measure hCG on a different assay 2

Critical Management Points

• Never use hCG value alone to exclude ectopic pregnancy, as approximately 22% of ectopic pregnancies occur at hCG <1,000 mIU/mL 2
• Never defer ultrasound based on "low" hCG levels in symptomatic patients, as ectopic rupture can occur at any hCG level 2
• Markedly elevated hCG (>100,000 mIU/mL) at 6 weeks may indicate gestational trophoblastic disease and requires immediate evaluation 2

Practical Algorithm for hCG Assessment

For pregnancy of unknown location with indeterminate ultrasound:

1. Obtain baseline quantitative serum hCG 2
2. Repeat hCG in exactly 48 hours to assess rise pattern 2
3. Perform transvaginal ultrasound regardless of hCG level 2
4. Continue serial monitoring until diagnosis is established 2

The pattern of hCG rise (or fall) combined with ultrasound findings determines pregnancy viability and location, not absolute weekly values 2, 4.