Nesidioblastosis: This condition is characterized by an excessive proliferation of pancreatic islet cells, leading to an overproduction of insulin. It is a common cause of hyperinsulinism in newborns, making it the most likely diagnosis.

Benign Insulinoma: Although less common in newborns, a benign insulinoma (a tumor of the pancreas that produces excess insulin) can cause hyperinsulinism. It's a consideration, especially if other causes are ruled out.
Glycogen Storage Disease: Certain types of glycogen storage diseases can lead to hyperinsulinism due to the abnormal regulation of glucose metabolism. However, they are less directly linked to hyperinsulinism compared to nesidioblastosis.

Malignant Insulinoma: Although rare in newborns, a malignant insulinoma would have severe implications for the child's health and prognosis. It's crucial to consider and rule out this diagnosis due to its potential impact on treatment and outcome.
Congenital Hyperinsulinism due to Genetic Mutations: Conditions like congenital hyperinsulinism due to mutations in genes such as ABCC8 or KCNJ11 can lead to severe hyperinsulinism. Missing these diagnoses could result in inadequate treatment and poor outcomes.

Beckwith-Wiedemann Syndrome: This genetic disorder can include features like macrosomia, omphalocele, and hyperinsulinism due to pancreatic islet cell hyperplasia. It's a rare condition but should be considered in the differential diagnosis of hyperinsulinism in a newborn, especially with other characteristic features.
Other Genetic Syndromes: Various genetic syndromes can include hyperinsulinism as part of their clinical presentation. These are rare and often associated with other distinctive features, but they should be kept in mind during a thorough diagnostic workup.