The correct answer is the time of birth. Explanation & Key Takeaways: • The testes descend into the scrotum at the time of birth. • Testicles form in the abdomen during foetal development. During the last couple of months of normal foetal development, the testicles gradually descend from the abdomen through a tube-like passageway in the groin into the scrotum. • Some babies have a condition called retractile testes and the healthcare provider may not be able to find the testicles. • Testicular descent occurs after the fourth month of foetal life. The testes are derived from the gonadal ridge medial to the mesonephric ridge of the intermediate cell mass. • The two phases of testes descent are regulated by a hormone secreted by Leydig cells: INSL3 that regulates the trans abdominal phase, whereas testosterone controls the inguinoscrotal phase.