Final answer:
The biggest challenge in nursing care of the client with hyperemesis gravidarum is managing the severe and persistent vomiting and its associated complications.
Step-by-step explanation:
The biggest challenge in nursing care of a client with hyperemesis gravidarum is managing the severe and persistent vomiting and its associated complications. Hyperemesis gravidarum is a condition characterized by excessive nausea and vomiting during pregnancy, which can lead to severe dehydration, electrolyte imbalances, and weight loss. Nurses will need to closely monitor the client's fluid and electrolyte status, administer intravenous fluids and medications as needed, and provide emotional support and education to the client and their family.