Human chorionic gonadotropin (hCG) is a hormone produced during pregnancy and is responsible in the preparation of endometrium for the implantation and the development of embryo in an early pregnancy. Once the fertilization takes place, the trophoblast cells which surround the developing embryo begin to produce and secrete hCG. hCG’s primary role is to keep the corpus luteum functioning, so that the corpus luteum continues to produce estrogen and progesterone. The presence of hCG can be detected in the maternal serum 7 days onwards after implantation.
The number of trophoblast cells during the early weeks of pregnancy represents level of hCG, while the number of cells in cleavage stage indicates the mitotic rate.
Higher rate of cells in cleavage stage resulting in a higher chance of hatching and implantation. According to a study by T.G Tanbo et al. , 2015, of the correlation between the number of embryo’s cells in cleavage stage, the number of oocytes retrieved, and maternal hCG concentration in 1,047 pregnancies; the transfer of 4-cell embryo gives higher hCG concentration than the transfer of 2-cell embryo, and the number of oocytes retrieved more than 20 compared to the fewer numbers yields lower hCG concentration significantly.
To sum up, hCG level in an early weeks of pregnancy is increased by the number of embryo’s cells in cleavage stage, and is decreased by the number of oocytes retrieved. Importantly, these two factors may have a great impact on embryo implantation.
By Navarat Siriprasertchok (Embryologist)