About

Human Chorionic Gonadotropin (hCG) is a glycoprotein hormone produced by syncytiotrophoblast cells after implantation. A quantitative serum β-hCG assay measures the hormone in mIU/mL and is the definitive biochemical confirmation of pregnancy. Misinterpretation of results is common because hCG concentrations vary by orders of magnitude across gestation: a value of 50 mIU/mL is normal at 3 weeks post-LMP but critically abnormal at 8 weeks. A single value rarely tells the full story. Serial measurements separated by 48 - 72 hours are required to assess viability via the doubling time (t_d). A normal intrauterine pregnancy typically shows a doubling time of 48 - 72 hours during the first 8 - 10 weeks. Slower rises may indicate ectopic pregnancy or nonviable gestation. This tool applies ACOG and clinical laboratory reference intervals to contextualize your result. It approximates interpretation assuming a singleton pregnancy with known last menstrual period. It does not replace physician evaluation, particularly for values in the discriminatory zone (1500 - 3000 mIU/mL) where ultrasound correlation is mandatory.

Formulas

The primary metric for early pregnancy viability is the hCG doubling time, calculated from two serial blood draws:

t_d = (t₂ − t₁) ⋅ ln(2)ln(hCG₂) − ln(hCG₁)

Where t_d = doubling time in hours, t₁ and t₂ = timestamps of the first and second blood draws (in hours), hCG₁ = first measured concentration (mIU/mL), and hCG₂ = second measured concentration (mIU/mL). A result of t_d between 48 and 72 hours is considered normal for viable intrauterine pregnancies below 6,000 mIU/mL. Above that threshold, the rate of rise slows physiologically and doubling time lengthens to 72 - 96 hours.

For single-value interpretation, the tool performs a range lookup: given gestational age w in weeks post-LMP and measured hCG, the result is classified as below range, within range, or above range relative to published 5th - 95th percentile intervals.

Reference Data

Weeks Post-LMP	Typical Range (mIU/mL)	Median (mIU/mL)	Clinical Notes
3	5 - 50	25	Implantation window; may be undetectable
4	5 - 426	100	Missed period expected; urine tests may turn positive
5	18 - 7,340	1,500	Gestational sac visible on transvaginal US at ≥ 1,500
6	1,080 - 56,500	12,000	Yolk sac and fetal pole expected
7 - 8	7,650 - 229,000	60,000	Cardiac activity should be present
9 - 12	25,700 - 288,000	100,000	Peak hCG; nausea often maximal
13 - 16	13,300 - 254,000	55,000	Plateau phase; levels begin declining
17 - 24	4,060 - 165,400	30,000	Second trimester; placenta sustains progesterone
25 - 40	3,640 - 117,000	20,000	Third trimester; gradual decline continues
Non-pregnant reference: < 5 mIU/mL
Discriminatory zone: 1,500 - 3,000 mIU/mL - intrauterine pregnancy should be visible on transvaginal ultrasound
Molar pregnancy: Often > 100,000 mIU/mL with abnormal US findings
Ectopic concern: Slower doubling (> 72 h) or plateau below discriminatory zone
Multiples: Values may be 30 - 50% higher than singleton ranges
Post-miscarriage: hCG should return to < 5 within 4 - 6 weeks

Frequently Asked Questions

Reference ranges assume ovulation at day 14 of a 28-day cycle. If ovulation occurred later (common with irregular cycles or cycles > 30 days), gestational age is overestimated and the HCG value will appear low relative to the stated week. Confirm dating with transvaginal ultrasound if there is discrepancy greater than 5 days.

A doubling time exceeding 72 hours in early pregnancy (hCG below 6,000 mIU/mL) raises concern for ectopic pregnancy or nonviable intrauterine pregnancy. However, approximately 15% of viable intrauterine pregnancies show slower-than-expected rises. Clinical correlation with ultrasound and progesterone levels is essential. A single slow rise is not diagnostic.

Yes. Exogenous hCG injections (e.g., Ovidrel, Pregnyl) used as trigger shots in IVF cycles produce detectable serum hCG for 10-14 days post-injection. Values drawn during this window reflect injected hormone, not embryonic production. Wait at least 14 days post-trigger before interpreting quantitative hCG as pregnancy-related.

The discriminatory zone is typically 1,500-3,000 mIU/mL for transvaginal ultrasound. Above this threshold, an intrauterine gestational sac should be visible. Absence of a sac above 3,000 mIU/mL strongly suggests ectopic pregnancy. The exact cutoff varies by institution and ultrasound equipment quality.

Twin pregnancies typically produce hCG levels 30-50% higher than singleton pregnancies at the same gestational age. However, overlap between singleton and multiple ranges is substantial. A high single hCG value alone cannot confirm multiples. Ultrasound confirmation is required after 5-6 weeks post-LMP.

Declining hCG before 10 weeks gestation typically indicates miscarriage or biochemical pregnancy. After the first trimester peak (9-12 weeks), declining levels are physiologically normal. Post-miscarriage, hCG should fall to below 5 mIU/mL within 4-6 weeks. Persistent elevation warrants evaluation for retained products or gestational trophoblastic disease.

Above 6,000 mIU/mL, the doubling time physiologically lengthens and becomes less reliable as a viability marker. At levels above 10,000 mIU/mL, the rise may slow to 96+ hours per doubling. At this stage, ultrasound findings (cardiac activity, crown-rump length) become the primary viability indicators rather than serial hCG kinetics.