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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 (In Vitro Fertilization) 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.