The nurse practitioner suspects congenital hypothyroidism because a 3-week-old infant presents with:

Rationale: A. A micropenis and jitterness are more characteristic of congenital hypopituitarism or other endocrine disorders, not primary congenital hypothyroidism. B. Vomiting, lethargy, and poor feeding are nonspecific and could indicate many neonatal conditions but do not specifically point to congenital hypothyroidism. C. Decreased activity, a large anterior fontanel, and poor feeding are classic signs of congenital hypothyroidism. Infants may also present with hypotonia, prolonged jaundice, constipation, and a hoarse cry. Early detection is critical to prevent growth retardation and intellectual disability. D. Rapid heart rate, irritability, and frequent stools are more suggestive of hyperthyroidism or other metabolic conditions, not hypothyroidism.