What does Hg stand for in medical nutrition terms?

My research shows that Hg on the Periodic Table represent the element Mercury, Which as we know is poisonous to humans and animals. However, in medicine Hg is possibly Hyperemesis gravidarum. More than 50% of all pregnant women experience some morning sickness, but only 2% develop hyperemesis gravidarum, a serious condition often leading to dehydration and malnutrition.

The exact cause of hyperemesis gravidarum is unknown,