Testicular descent usually occurs in 5th – 7th month of gestation, though can continue in the first few months of postnatal life.
~20% of undescended testes are impalpable, either due to being intra-abdominal or in the inguinal canal. If there are concerns regarding testicular presence, an ultrasound +/- karyotype is required in the postnatal period.
Smeulders, N., Wilcox, D.T. (2005). ‘Urinary tract anomalies’ in Rennie and Roberton’s Textbook of Neonatology 5th edition, Chapter 35, page 948.