Approximately 3% of full-term baby boys have undesended testis at birth.
50 - 65% of these testes descend sponateously over the next 6 months. Up to 30% of premaure baies have undescended testes at birth and again most of these descend spontaneously during their first year. However, overall udts are more common in ex-preemies. Also more common inboys concieved by ivf.