Human chorionic gonadotrophin (HCG)
HCG is the most likely endocrine factor which accounts
for the development of HG. This conclusion is based on
observed associations between increased production of
HCG (as in molar or in multiple pregnancies) [13-15] and
the fact that the incidence of hyperemesis is highest at the
time when HCG production reaches its peak during preg-
nancy (around 9 weeks gestation) [13]. However, there is
no evidence to support this hypothesis and some preg-
nant women do not experience nausea and vomiting
despite elevated HCG-levels. In addition, patients suffer-
ing from chorionic carcinoma - a disease that is also asso-
ciated with an increase in HCG - do not usually
experience vomiting. These controversial findings may be
caused by the varying biological activity of different iso-
forms of HCG as well as an individual sensitivity for eme-
togenic stimuli. Additionally, hormone-receptor
interactions may modify the effects of HCG leading to
hyperemesis in some cases but having no emetic conse-
quences in others [5]