When you finally get
pregnant, the doctor will monitor the health of your
pregnancy by measuring your beta HCG ( also known as
beta) levels. A pregnancy should be documented as early
as possible. This is important, because appropriate
care and precautions can then be taken at an early stage.
The most sensitive, accurate and reliable pregnancy
test is a blood test for the presence of beta HCG (human
chorionic gonadotropin), often just called "beta".
The HCG is produced by the embryo, and is the embryo's
signal to the mother that pregnancy has occurred. Beta
HCG levels vary according to the gestational age. In
a non-pregnant woman, they are less than 10 mIU/ml.
They are typically about 100 mIU/ml 14 days after ovulation
in a healthy singleton pregnancy. They should double
every 48- 72 hours in a healthy pregnancy.
The levels are higher in a multiple pregnancy; and if
the levels don't double as expected, this suggests that
the pregnancy is unhealthy. Possibilities include a
non-viable intrauterine pregnancy which will miscarry;
or an
ectopic pregnancy. If the beta HCG level is more than
1000 mIU/ml, and the doctor cannot see a pregnancy sac
in the uterine cavity on vaginal ultrasound scan, then
it's
possible you have an ectopic pregnancy. Beta HCG levels
can be measured in the blood by RIA (radioimmunoassay)
, CLIA (chemiluminescent assay) and DELFIA ( fluorescent
immunoassay) testing; and positive levels (more than
10 mIU/ml) in the blood can be detected as early as
2 days before the period is missed. In the old days,
the only way of determining the presence of HCG was
by testing the urine, i. e, by using urine pregnancy
test kits. Modern urine pregnancy kits (using monoclonal
antibody technology ) are now quite sensitive and can
detect a pregnancy as early as 1 to 2 days after missing
a period (at a blood HCG level of about 50 to 100 mIU/ml).
The benefit of urine pregnancy test kits is that they
are less expensive; and testing can be done at home
by the patient herself. However, instructions need to
be followed carefully, and errors in interpreting the
test results are not uncommon. These errors could occur
if the urine is too dilute; or if the test is not done
properly; or if there is a urinary tract infection exists.
The major advantage of blood tests is the fact that
they measure the actual level of the HCG in the blood
- and this factor can be very helpful in managing pregnancy
problems, if they occur. Most clinics start testing
beta HCG levels about 14 - 16 days after egg collection;
and repeat the test every 48-72 hours. As the embryo
grows rapidly, HCG levels normally double every 2 to
3 days. Thus, one reliable sign of a healthy pregnancy
is the fact that the HCG levels are increasing rapidly,
and often doctors will measure serial beta HCG levels
3 days apart in order to determine the viability of
the pregnancy. A rising HCG level is reassuring. Typically,
in a healthy singleton pregnancy, the beta HCG level
is about 100 mIU/ml about 16 days after ovulation, though
this level can vary considerably. The levels are higher
in multiple pregnancies; and lower in non-viable pregnancies
and ectopic pregnancies.
Problems with HCG testing can occur if you have earlier
been given HCG (human chorionic gonadotropin) injections
for inducing ovulation. Normally, this exogenous HCG
is excreted by the body in 10 days; but sometimes it
can linger on. This is why, if the HCG level is very
low, the test may need to be repeated, to confirm that
the level is increasing. If the positive test result
is because of the HCG injection, the level will decline.
If you are pregnant, the HCG level should rise.
What are "biochemical pregnancies" ? These
are pregnancies in which the HCG test is positive after
the period has been missed; the levels increase, but
are still low; and no pregnancy is ever documented on
ultrasound. Biochemical pregnancies are often seen after
IVF and GIFT. While they are not clinical pregnancies,
they are of useful prognostic information, because they
may mean that your chance of getting pregnant in a future
cycle are good.
One drawback with the HCG test is that a positive HCG
simply means a pregnancy is present in the body - it
does not provide any information about the location
of this pregnancy, which may be tubal or ectopic.
During the very early pregnancy, HCG levels are the
only way of monitoring the pregnancy. HCG levels which
do not increase as rapidly as they should may mean that
there is a problem with the pregnancy - the embryo may
miscarry because it is unhealthy; or the pregnancy could
be an ectopic pregnancy. Differentiating between the
two conditions is obviously important, and this is where
vaginal ultrasound plays a key role.
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