hCG (human chorionic gonadotropin) is a hormone made by trophoblast cells of the early embryo. It maintains progesterone production in early pregnancy and is the hormone pregnancy tests detect.

When does hCG peak in pregnancy?

hCG typically peaks around weeks 8 to 10 of pregnancy, then declines to a lower plateau for the rest of pregnancy. This decline is normal.

HCGCALCULATOR.COM

hCG: The Complete Picture

What the pregnancy hormone is, how it behaves, and everywhere else it matters in medicine.

WHAT HCG IS

hCG (human chorionic gonadotropin) is a hormone made by trophoblast cells — the cells of the early embryo that will become the placenta. Its main job is to tell the ovary's corpus luteum to keep producing progesterone, which maintains the uterine lining until the placenta can support the pregnancy on its own.

hCG is built from two pieces: an alpha subunit identical to the one in LH, FSH, and TSH, and a beta subunit unique to hCG. That is why blood and urine tests measure the beta subunit — the part that cannot be confused with anything else. It is also why you often see it written as “β-hCG.”

HOW HCG BEHAVES IN PREGNANCY

In a healthy early pregnancy, hCG rises fast — roughly doubling every 2 to 3 days at first, then more slowly as levels climb. Levels typically peak around weeks 8 to 10 of pregnancy, then decline and settle at a lower plateau. This is normal: falling hCG after week 10 does not mean something is wrong.

Because absolute values vary enormously between healthy pregnancies, single hCG numbers are rarely useful. The pattern of change between two tests is what carries information — which is exactly what our calculator evaluates against every major published threshold.

WHERE ELSE HCG MATTERS

hCG is far more than a pregnancy test:

• Cancer marker: hCG is a key tumor marker for gestational trophoblastic disease (including molar pregnancy) and for germ cell tumors of the testis and ovary. A positive hCG in a man, or in a woman who is not pregnant, always deserves an explanation.

• Prenatal screening: hCG (or free β-hCG) is one of the blood markers in first-trimester combined screening and the second-trimester quad screen.

• Fertility treatment: injectable hCG (Ovidrel, Pregnyl, Novarel) is used as a “trigger shot” to cause ovulation, because hCG mimics the natural LH surge. See our trigger shot clearance guide.

• Men's health: hCG stimulates testosterone and sperm production in some men with hypogonadism. It is prohibited for male athletes by the World Anti-Doping Agency.

• The pituitary gland: small amounts of hCG can come from the pituitary, especially around and after menopause — a common source of confusing low-positive tests.

• The thyroid: because hCG resembles TSH, very high levels (twins, molar pregnancy, severe morning sickness) can temporarily overstimulate the thyroid.

GO DEEPER

Every page below is built the same way: plain language, every number traceable to a verified primary source.

• The implantation delay — why hCG appears only after implantation, with the full timeline and graph.

• When to test — a calculator built from the implantation evidence.

• False positives — phantom hCG, pituitary hCG, trigger shots, and more.

• False negatives — testing too early, dilute urine, and the hook effect.

• Test marketing — what “99% accurate” actually means.

• IVF beta calculator — interpreting your beta after embryo transfer.

• hCG levels by week — verified reference tables, and why single values mislead.

• Slow-rising hCG — what a below-average rise really means.

• hCG after miscarriage or abortion — how long to zero, and when to worry.

• Chemical pregnancy — the earliest losses, explained with compassion.

• Ectopic pregnancy and hCG — the patterns, and the symptoms that mean go in now.

• hCG and twins — can a high number diagnose twins? (No.)

• The hCG diet — the weight-loss fraud, debunked with the primary evidence.

• The discriminatory zone — for clinicians: PUL management and why 3,500 replaced 1,500.

• Molar pregnancy — extreme hCG, the follow-to-zero rule, and near-100% cure rates.

• Multi-draw curve tool — three or more values, one fitted trend with a plotted curve.

• hCG in men — tumor marker, medication, and the gray market.

KEY SOURCES

1. Wilcox AJ, Baird DD, Weinberg CR. Time of implantation of the conceptus and loss of pregnancy. N Engl J Med. 1999;340(23):1796-1799.

2. Larraín D, Caradeux J. β-Human chorionic gonadotropin dynamics in early gestational events: a practical and updated reappraisal. Obstet Gynecol Int. 2024;2024:8351132.

3. Gnoth C, Johnson S. Strips of hope: accuracy of home pregnancy tests and new developments. Geburtshilfe Frauenheilkd. 2014;74(7):661-669.

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