Q. Why does pregnancy sickness last so long in some pregnancies?
We cannot give a definite answer to this important question at present. However, we have mentioned in the short answer that there are at least 5 different forms of the hormone human chorionic gonadotrophin (hCG), the acidic form having the longer half life in maternal blood being the dominant form until the 11 th to the 15 th week of pregnancy. This form of hCG has been related to pregnancy sickness symptoms. It is speculated that this acidic form of hCG is produced within placental (after-birth) cells by the effect of the intracellular enzymes glycosidases and glycosyltransferase acting on intracellular precursors of hCG. Deletion of sialyl-transferase and increased sialidase activity are considered likely causes of the production of the acidic form of hCG.. To get a better understanding we need to investigate the blood samples of women who are having these prolonged symptoms of pregnancy sickness to find out if these assumptions bear any relationship to the truth.