Final answer:
Hyperemesis Gravidarum is the severe form of nausea and vomiting that can occur after week 16 of pregnancy, requiring medical attention.
Step-by-step explanation:
The severe form of nausea and vomiting (N/V) that occurs after week 16 of pregnancy is known as Hyperemesis Gravidarum (A). This condition is not to be confused with typical morning sickness, which usually subsides by about week 12. Hyperemesis Gravidarum can lead to severe dehydration and requires medical attention. Morning Sickness (B), on the other hand, is generally less severe and resolves earlier in the pregnancy. Neither Gestational Diabetes (C) nor Preeclampsia (D) is characterized by severe N/V in the second trimester; these conditions have different symptoms and complications.