Human Chorionic gonadotropin or HCG, is a hormone released when a woman is pregnant. As soon as the embryo implants itself on the uterine wall, this hormone is produced which gives an indication that a fertilization has taken place.
It can be detected through a blood or urine test as early as 11 days after conception much before a woman misses her period. As soon as pregnancy starts, the level of HCG in the blood keep doubling every 2-3 days reaching its peak by 8-11 weeks and then slowly reducing to remain stable throughout the rest of the pregnancy.
The health of the pregnancy is determined by the rate at which the HCG levels increase in the first trimester. There are cases when the level of HCG in the blood is low. There are various reasons for this and each needs to be seen on a case to case basis. Low HCG levels in the second and third trimester are not of much concern unlike the first trimester. So then what does a low HCG level in the first trimester mean?
A low HCG level of <5mlU/ml usually is a sign of negative pregnancy. In case you think you are pregnant or have any of the symptoms related to pregnancy like nausea, vomiting, breast tenderness; wait for a couple of days before repeating the test. Since HCG levels double every 48 hours repeating the test after a day or two will give definite results as to the state of pregnancy.
Ideally, it is advisable to wait till you miss a period to get a more authentic report. In some cases, you may get a positive result at the start of the pregnancy. And then the HCG levels remain low or the rate at which they increase may be too slow. This may indicate a blighted ovum or what is commonly called anembryonic pregnancy.
In this situation the egg attaches itself to the uterine wall but does not develop into an embryo. A woman may have all the symptoms of pregnancy till an ultrasound determines an empty womb or an empty sac. In case of an ectopic pregnancy, low levels of HCG are detected. The levels may be normal at the start but may not increase at a healthy rate.
Ectopic pregnancies happen when the fertilized egg attaches itself outside the uterine wall. Since the uterus lining does not detect a growing embryo, its stops growing thus resulting in low HCG levels. In most cases, a low HCG level could be a simple miscalculation of the pregnancy date. But as the pregnancy progresses, the rate of increase of the HCG hormone in the blood may indicate whether the pregnancy is healthy or not.
All the above could contribute to low HCG levels in pregnant women, but low HCG levels need not always end in miscarriage though the chances are high. In many cases, even with low HCG levels, women have had healthy pregnancies and given birth to perfectly healthy babies. Though a low HCG level is a cause of concern, it is not the ultimate measure for a safe pregnancy. An ultrasound examination at the 5-6th week will say more appropriately how the pregnancy is progressing.