If you are pregnant or trying to conceive, you have likely heard about HCG — the "pregnancy hormone." HCG levels are used to confirm pregnancy, monitor its progress, and can provide important information about your baby's health. Understanding what HCG is, how levels change throughout pregnancy, and what different values mean can help you navigate this exciting time with greater confidence.

What Is HCG?

HCG stands for Human Chorionic Gonadotropin. It is a hormone produced by cells that form the placenta after a fertilised egg implants in the uterine wall. HCG is what pregnancy tests detect — both home urine tests and blood tests.

Key functions of HCG:

Signals the body that pregnancy has occurred

Maintains the corpus luteum, which produces progesterone

Supports the uterine lining during early pregnancy

Helps prevent the immune system from rejecting the developing embryo

For more about blood pregnancy tests, read our comprehensive guide to blood pregnancy tests.

HCG Blood Tests vs Urine Tests

### Urine Tests (Home Pregnancy Tests)

Detect the presence of HCG

Provide a yes/no answer

Can detect pregnancy from around the time of a missed period

Convenient but less sensitive than blood tests

### Blood Tests (Quantitative HCG)

Measure the exact amount of HCG in your blood

More sensitive — can detect pregnancy earlier

Allow tracking of HCG levels over time

Provide more detailed information about pregnancy progress

Can detect very early pregnancy loss

Normal HCG Levels During Pregnancy

HCG levels vary enormously between individuals and change dramatically throughout pregnancy. Here are typical ranges:

### First Trimester

Weeks 3-4 (1-2 weeks after conception):

5 to 50 mIU/mL

Just detectable; pregnancy may not yet show on urine tests

Weeks 4-5:

5 to 426 mIU/mL

HCG rising rapidly; most urine tests will be positive

Weeks 5-6:

18 to 7,340 mIU/mL

Continuing rapid rise

Weeks 6-7:

1,080 to 56,500 mIU/mL

Peak levels approaching

Weeks 7-8:

7,650 to 229,000 mIU/mL

Near or at peak levels

Weeks 9-12:

25,700 to 288,000 mIU/mL

Levels plateau then begin to decline

### Second and Third Trimesters

Weeks 13-16:

13,300 to 254,000 mIU/mL

Declining from peak

Weeks 17-24:

4,060 to 165,400 mIU/mL

Continued gradual decline

Weeks 25-40:

3,640 to 117,000 mIU/mL

Relatively stable until birth

Important note: These ranges are approximate. There is enormous variation between healthy pregnancies, so individual values should always be interpreted by a healthcare professional.

The Importance of HCG Doubling Time

In early pregnancy, HCG levels typically double every 48 to 72 hours. This doubling time is often more informative than a single HCG value.

What doubling time indicates:

Normal doubling (48-72 hours): Suggests healthy pregnancy progression

Slower than expected rise: May warrant further investigation but does not always indicate a problem

Very rapid rise: Could indicate multiple pregnancy

Falling levels: May indicate pregnancy loss or ectopic pregnancy

To assess doubling time, two or more blood tests are taken 48-72 hours apart.

When Are HCG Levels Checked?

### Early Pregnancy Confirmation

Blood HCG tests can confirm pregnancy earlier than urine tests — sometimes as early as 6-8 days after ovulation.

### Monitoring High-Risk Pregnancies

Serial HCG testing may be recommended for:

Women with history of miscarriage

Pregnancies following fertility treatment

Suspected ectopic pregnancy

Bleeding in early pregnancy

### Screening Tests

HCG levels are measured as part of prenatal screening tests, including:

First trimester combined screening

Quadruple test in the second trimester

Non-invasive prenatal testing (NIPT)

What Do Abnormal HCG Levels Mean?

### Low HCG Levels

Lower than expected HCG may indicate:

Miscalculated dates — Pregnancy may be earlier than thought

Ectopic pregnancy — Pregnancy outside the uterus

Impending miscarriage — Especially if levels are falling

Blighted ovum — Fertilised egg that did not develop properly

Important: A single low HCG value does not diagnose any of these conditions. Serial measurements and ultrasound are usually needed.

### High HCG Levels

Higher than expected HCG may indicate:

Multiple pregnancy — Twins or more

Miscalculated dates — Pregnancy may be further along

Molar pregnancy — Abnormal growth of placental tissue (rare)

### Slowly Rising HCG

HCG that rises but does not double appropriately may indicate:

Ectopic pregnancy

Pregnancy that may not be viable

Normal pregnancy (in some cases)

Slow rise requires careful monitoring and clinical judgement.

HCG and Pregnancy Symptoms

HCG is responsible for many early pregnancy symptoms:

Nausea and vomiting — Often correlate with HCG levels

Breast tenderness

Fatigue

Frequent urination

Symptoms often peak when HCG peaks (around weeks 8-11) and may improve as levels decline in the second trimester. For more about early pregnancy signs, read our article on common signs of early pregnancy.

HCG After Pregnancy Loss

After miscarriage or pregnancy termination, HCG levels gradually decline. Monitoring this decline ensures that:

All pregnancy tissue has passed

No complications have occurred

The body is returning to non-pregnant state

HCG typically returns to non-pregnant levels (<5 mIU/mL) within 4-6 weeks, though this varies.

Understanding Your Results

When interpreting HCG results, remember:

Wide normal ranges — There is huge variation between healthy pregnancies

Trends matter more than single values — Serial measurements are more informative

Clinical context is essential — Results must be interpreted alongside symptoms and ultrasound findings

Do not compare with others — Every pregnancy is different

HCG Testing in London

At Private Blood Tests London, we offer quantitative HCG blood testing at our CQC-registered clinic in South Kensington. Whether you need early pregnancy confirmation, serial monitoring, or follow-up testing, we provide fast, accurate results with same-day or next-day turnaround.

Our experienced team understands the anxiety that can accompany pregnancy testing, and we provide compassionate, confidential care throughout the process.

For more information about pregnancy-related testing, read our guide to [blood pregnancy tests](/blog/what-is-blood-pregnancy-test-how-it-works-a-simple-guide) and explore our [comprehensive health screening packages](/health-screening).

Book your HCG blood test today and get the answers you need.

What You Should Know About HCG Levels During Pregnancy