Scientists have identified six new genetic links behind extreme morning sickness. In the largest genetic study of hyperemesis gravidarum (HG) to date, a research team from the Keck School of Medicine of the University of South Carolina and international collaborators analyzed genetic data from nearly half a million women. The study, published in Nature Genetics, examined 10,974 women who experienced HG and compared them with 461,461 controls across European, Asian, African and Latino ancestries.