system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
Which of the following is the most common tumor of the fetus and newborn –
assistant
The correct answer is  Sacrococcygeal Teratoma (SCT) is the most common neoplasm in the fetus and newborn.

Sacrococcygeal Teratoma (SCT) is the most common neoplasm in the fetus and newborn with an estimated prevalence of 1:30,000- 1:40,000 and with a 3:1 female preponderance. - Handbook of Fetal Medicine by Shailesh Kumar (Cambridge Univ Press) 2010/87

Most common tumor in fetus and neonate → sacrococcygeal teratoma
Most common tumor in infancy → neuroblastoma