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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. As the embryo grows rapidly, HCG levels normally double every two to three days. Thus, one reliable sign of a healthy pregnancy is the fact that the HCG levels are increasing rapidly, and often doctors may need to measure two HCG levels three days apart in order to determine the viability of the pregnancy. A rising HCG level is reassuring.
Problems with HCG testing can occur if you have earlier been given HCG (human chorionic gonadotropin) injections for inducing ovulation. Normally, the body excretes this exogenous HCG 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.
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 do provide 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 early pregnancy, HCG levels are the only way of monitoring the pregnancy. HCG levels that do not increase as rapidly as they should, could 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.
With vaginal ultrasound, it is possible to detect a pregnancy as early as two to four days after a missed period. An early pregnancy is observed as a pregnancy sac or gestational sac in the uterine cavity. The uterine lining appears thick and bright white, and the sac appears as a black bubble in this lining. The sac should grow (at the rate of about 1 mm per day) and, if it does so, this is reassuring. The sac represents only the placental tissue - the embryo is so tiny at this stage that it cannot be seen on ultrasound. At six weeks of pregnancy, an echo can be seen within the sac; this is the embryo. This grows rapidly, so that on scans done by eight weeks, one should be able to see a beating fetal heart as well. This is very good evidence of a healthy fetus and the chances of a problem occurring in pregnancy after this point are small.
© Dr. Aniruddha Malpani and Dr. Anjali Malpani www.drmalpani.com
Credits: How to Have a Baby: Overcoming Infertility
