Se HCG is a hormone mainly released by the trophoblastic (placental) tissue. It is an essential hormone marker in early pregnancy and detectable following embryo implantation. The presence of this hormone in the blood and subsequently in the urine by the third week post implantation forms the basis of the urine pregnancy test.
Se HCG discriminatory level and diagnosis of early pregnancy
The main use of this test is to indicate the presence of pregnancy tissue. The detection of se HCG precedes ultrasonography evidence of a gestation (pregnancy) sac. The general threshold for the presence of a gestation sac on ultrasound is approximately 2000iu/L (Barnhart 1999). When the se HCG exceeds this threshold, the gestational sac must be seen in the uterine cavity for a normal pregnancy. Failure to observe this is an indication of ectopic pregnancy, until proven otherwise.
In clinical practice, most doctors would order a Se HCG when the pelvic ultrasound failure to demonstrate a pregnancy sac following a positive urine pregnancy test (UPT). If the se HCG level is above the threshold for detection by ultrasonography, then ectopic pregnancy must be excluded.
A slow rising Se HCG and diagnosis of a viable pregnancy
It is a known adage that a rising se HCG indicates a viable intrauterine pregnancy. Kadar (1990) had shown that a hormonal rise of at least 66% over 2 days is highly predictive of a healthy pregnancy. Failure to observe the ‘doubling effect’ could indicate an abnormally developing pregnancy, ectopic pregnancy or impending miscarriage.
Declining or flattening HCG levels
When the result of HCG flattens or decline, it certainly describes a failed or non- viable pregnancy. Barnhart (2004) had found that declining HCG level is quadratic and exhibits a faster decline when the initial se HCG is higher.
An abnormally high Se HCG
It can also indicate multiple pregnancy or abnormal placental tissue (trophoblastic tissue) when the serum level is excessive higher than expected. This observation is explained by the presence of a larger placental tissue, producing more HCG hormone as in multiple pregnancy and abnormal trophoblast cells with autonomous hormone production.
Se HCG is a useful additional test useful in the diagnosis of early pregnancy and its complications.
Barnhart KT et al., Obstet Gynecol (2004)
Barnhart KT et al., Obstet Gynecol (1999)
Kadar et al., Fert Steril (1990)