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What you should know about HCG levels during pregnancy

The level of human chorionic gonadotropin hormone (HCG) rises rapidly during the first trimester of pregnancy, but the HCG levels may vary significantly between pregnant women.

The human chorionic gonadotropin hormone (HCG), also called beta human chorionic gonadotropin (b-HCG), is the most known hormone during pregnancy. The information below will help you understand the HCG levels in pregnancy.

What is HCG?

HCG hormone is a hormone synthesised in the placenta. The level of this hormone rises rapidly during the first trimester of pregnancy and is usually detectable in urine within 1 – 2 days after egg implantation.

When you urinate on a home pregnancy test, it measures your HCG levels.

How does the level of HCG change during pregnancy?

HCG is produced after implantation of the embryo in the uterine lining. The implantation usually occurs six days following ovulation but may also take about 12 days. Other hormones increase at the onset of pregnancy and continuously rise through the 4-weeks of pregnancy, but HCG does not follow this pattern.

The HCG hormone doubles in concentration every 29 – 50 hours in the first weeks of pregnancy, but after weeks 8 – 10, HCG levels will gradually fall. This means, at the onset of pregnancy, your HCG level measures in IU/l or mIU/ml may measure two, then four, eight, 16 and spike to the 25,000 to 50,0000 range. When the HCG level reaches 100,000, it gradually decreases and remains about 10,000 throughout the pregnancy.

Most experts believe that the changes in HCG levels are due to the placenta taking over the production of progesterone and oestrogen at some point in the pregnancy, meaning the HCG no longer needs to stimulate the ovaries to produce these hormones.

What tests are available for HCG levels?

Home pregnancy tests are available for measuring HCG levels in urine. These urine pregnancy tests give an accurate result and can detect HCG levels between 20 – 50mIU/Ml. If you have a positive result from a beta HCG test UK, you still need confirmation with pelvic ultrasound, blood test or pelvic exam at your doctor’s office.

A blood test for pregnancy can give a positive result even with low levels of HCG, as it can measure about 1 – 5mIU/mL of HCG. However, only one blood test isn’t reliable, so you need at least two blood tests 48 hours apart to understand the pregnancy’s progress because the pattern of increase in HCG levels is more important than the numbers.

Why do HCG levels fluctuate?

HCG hormone is unique because it has a wide range of what is considered normal. Due to the wide range of normal HCG levels, it’s usually difficult to determine pregnancy progress with HCG levels.  

A low or high HCG level may indicate a normal pregnancy, but doctors can use its increasing pattern to assess the pregnancy. In a normal pregnancy, the HCG levels will double every 48 hours, peaking at about 90 – 100mIU/mL. If the HCG level is significantly lower or higher, the Ob-Gyn will need to check the pregnancy.

What is the cause of low HCG levels?

Low HCG levels may indicate an early pregnancy or the end of a pregnancy in miscarriage. Other causes of low HCG levels are:

  • Ectopic pregnancy is where the embryo implants outside the uterus, often in the fallopian tube
  • Blighted ovum where the fertilised egg doesn’t develop properly

In some cases, inaccurately estimated gestational age may be the cause, meaning the pregnancy isn’t far gone as believed. This may be when a woman has an irregular menstrual cycle and doesn’t ovulate on day 14 of each menstrual cycle.

What is the cause of high HCG levels?

Extremely high HCG levels, usually above 100,000, may indicate an abnormal pregnancy resulting from molar pregnancy or placental tumour, where a non-viable egg implants in the uterus, secreting HCG hormone.

A high level of HCG may indicate multiple pregnancies or inaccurate measurement of gestational age, meaning the pregnancy may be far gone than expected.

For a beta HCG blood test near me, visit Private Blood Tests London or call 020 7183 0244 to book an appointment for your testing.