**Urinary B-HCG Essential**
Info:
hCG = human chorionic gonadotrophin
Where is hCG produced?
hCG is produced by the placenta. It enters the blood stream as soon as implantation happens, approximately one week after fertilization and ovulation, when the embryo implants and the placenta attaches to the uterine lining.
What is its role?
Initially hCG maintains the corpus luteum's secretion of progesterone and oestrogen. Later in pregnancy it may have a role in regulating placental oestrogen secretion and in modulating the maternal immune response.
How is it measured?
hCG is measured in milli-international units per milliliter (mIU/ml)
Levels can be measured in the urine or in the blood stream (serum). Urine levels are usually lower than serum hCG levels.
Serum hCG v urine B-hCG
Serum hCG
Sensitive
Pregnancy detected ~2-3 days after implantation or 8-9 days after fertilization
hCG level (mIU/ml) | Result |
<5 | negative |
>25 | positive |
5 - 25 | equivocal |
Urine B-hCG
Qualitative (results are either "positive" or "negative")
Less sensitive, positive results a few days later than serum hCG
How does hCG change over preganancy?
In 85% of normal pregnancies the hCG level willvdouble every 48 - 72 hours.
As the pregnancy progresses the hCG level increases, therefore, the doubling time increases to approx 96 hours.
A maximum level is usually reached by the 10th or 11th week, after this hCG normally decreases.
Why do we measure hCG?
hCG monitoring is useful to assess the pregnancy before the fetal heart is seen (ie before 6-7 weeks after LMP).
It is usually done to rule out an ectopic pregnancy or an early miscarriage.
Miscarriages and ectopic pregnancies are likely to show lower levels and slower rises in hCG.
hCG levels >1000-1500 mIU/ml USS usually identifies an intrauterine pregnancy.
Take Note!
Normal levels of hCG vary tremendously.
After 5-6 weeks of pregnancy, USS is much more predictive of pregnancy outcome than hCG levels.
Once the fetal heart is seen, most doctors will monitor this rather than hCG levels.