Hormone Test
Human Chorionic Gonadotropin (hCG) Test
A comprehensive guide to the hCG blood test: how it confirms pregnancy, what serial values reveal about early pregnancy viability, and how synthetic hCG functions in IVF treatment.
Test Overview
Human chorionic gonadotropin (hCG) is produced by trophoblast cells of the developing embryo beginning shortly after implantation. It is the hormone pregnancy tests detect and the primary hormonal signal that sustains the corpus luteum during the first trimester.
Key Timing
A quantitative blood beta-hCG can detect pregnancy as early as 8 to 11 days after ovulation or embryo transfer. In IVF, most clinics test between Day 9 and Day 14 after transfer. Home urine tests typically turn positive around the time of a missed period.
1. Purpose and uses of the hCG test
In pregnancy detection and monitoring
- Confirm pregnancy through qualitative (positive/negative) or quantitative (exact level) measurement.
- Monitor early pregnancy viability through serial measurements drawn 48 hours apart.
- Investigate suspected ectopic pregnancy: abnormal hCG rise patterns or plateau may indicate implantation outside the uterus.
- Detect pregnancy loss: a falling hCG after a confirmed positive indicates miscarriage or biochemical pregnancy.
- Screen for molar pregnancy: hCG levels significantly above the expected range for gestational age can indicate abnormal placental growth.
In IVF and fertility treatment
- Trigger injection: synthetic hCG is administered to complete final egg maturation before retrieval as part of the IVF process, mimicking the natural LH surge.
- Luteal phase support: low-dose hCG is used in some protocols to supplement progesterone production after egg retrieval.
- Post-transfer confirmation: a blood beta-hCG drawn 9 to 14 days after embryo transfer confirms whether implantation has occurred.
2. Types of hCG tests
Two distinct test types are used depending on the clinical question.
| Test type | What it measures | When it is used |
|---|---|---|
| Qualitative hCG | Presence or absence only (positive/negative) | Initial pregnancy confirmation; home urine tests |
| Quantitative beta-hCG | Exact hCG concentration (mIU/mL) | IVF monitoring; ectopic investigation; viability tracking |
The quantitative test is performed exclusively as a blood draw and is more sensitive than urine-based methods. It can detect hCG at levels as low as 1 to 2 mIU/mL, several days before a home test would register a positive result.
3. How hCG works in early pregnancy
Within 6 to 8 days of fertilization, the embryo's outer layer (trophoblast) begins secreting hCG. The hormone binds to receptors on the corpus luteum, the structure that forms in the ovary after the follicle releases its egg. This binding prevents the corpus luteum from regressing, which would otherwise cause progesterone levels to fall and menstruation to begin.
Sustained progesterone from the corpus luteum maintains the uterine lining and supports the implanted embryo until the placenta is fully developed and capable of independent hormone production, typically around weeks 10 to 12.
hCG and the immune system
hCG also plays a role in immune tolerance of the embryo. It promotes the expansion of regulatory T cells in the uterus, helping the maternal immune system recognize and protect the developing embryo rather than treating the paternal genetic material as foreign tissue.
4. hCG levels by gestational week
The following ranges reflect population data for singleton pregnancies. Individual variation is wide. A single value is less informative than the trend over time.
| Weeks from last menstrual period | Typical hCG range (mIU/mL) | Clinical note |
|---|---|---|
| 3 weeks | 5 to 50 | Very early; may not register on urine test |
| 4 weeks | 5 to 426 | Wide overlap; serial testing more useful |
| 5 weeks | 18 to 7,340 | Fetal heartbeat may be visible on ultrasound |
| 6 weeks | 1,080 to 56,500 | Heartbeat usually confirmed |
| 7 to 8 weeks | 7,650 to 229,000 | Rapid rise phase |
| 9 to 12 weeks | 25,700 to 288,000 | hCG peaks; placenta beginning to take over |
| 13 to 16 weeks | 13,300 to 254,000 | Gradual decline begins |
| 17 to 24 weeks | 4,060 to 165,400 | Plateaued second trimester levels |
5. Interpreting serial hCG results: the 48-hour rule
A single hCG value confirms a pregnancy exists. Serial measurements, drawn 48 hours apart, reveal whether the pregnancy is progressing as expected.
Normal rise
In a healthy intrauterine pregnancy, hCG rises by at least 53% over 48 hours during the first 6 to 7 weeks. Many clinicians still use the term doubling, but the minimum acceptable rise is 53%, not 100%.
Slow rise
A rise of less than 53% over 48 hours warrants concern. It may indicate an ectopic pregnancy, a failing intrauterine pregnancy, or a pregnancy of unknown location. Additional blood tests and ultrasound evaluation are used to clarify the diagnosis.
Plateau or decline
An hCG level that stops rising or falls before week 10 indicates the pregnancy is not progressing. This may reflect a miscarriage, a blighted ovum, or an ectopic pregnancy requiring prompt medical evaluation.
Values above the normal range
hCG significantly above the expected range for gestational age may indicate a multiple pregnancy (twins or triplets produce proportionally higher hCG) or, less commonly, a molar pregnancy.
6. hCG in IVF: the trigger shot
In an IVF cycle, the hCG trigger injection replaces the natural LH surge that would normally cause final egg maturation. The standard protocol schedules egg retrieval exactly 34 to 36 hours after the trigger is administered.
Standard hCG trigger
Urinary hCG (e.g., Pregnyl) or recombinant hCG (e.g., Ovitrelle) at doses of 5,000 to 10,000 IU are most commonly used. Because hCG has a long half-life, it provides sustained stimulation over the 36-hour window before retrieval.
GnRH agonist trigger: an alternative for high-risk patients
Patients with a high AFC or high AMH who are at significant risk of ovarian hyperstimulation syndrome (OHSS) may receive a GnRH agonist trigger instead of hCG. This produces a shorter and self-limiting LH-like surge, reducing ovarian overstimulation. In these cases, embryos are typically frozen rather than transferred fresh.