In the first several weeks after the egg is fertilized, the embryo develops early sex organs. In the male, if the early testes fail to develop before 8 weeks into the pregnancy, the baby will have female genitals.
If the testes are lost between 8 and 10 weeks, the baby will be born with ambiguous genitalia. This means the child will have parts of both male and female genitals.
However, if the testes are lost after the time when the male genitals differentiate (between 12 and 14 weeks), the baby will have normal male genitals (penis and scrotum), but no testes. This is known as congenital anorchia, or the "vanishing testes syndrome."
The cause is unknown, but in some cases there are genetic factors.
Call your health care provider if your male child appears to have extremely small or absent testicles or does not appear to be entering puberty during his early teens.
Lambert SM, Vilain EJ, Kolon TF. A practical approach to ambiguous genitalia in the newborn period. Urol Clin North Am. 2010 May;37(2):195-205.
Achermann JC, Hughes JA. Disorders of sex development. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 11th ed. Philadelphia, Pa: Saunders Elsevier; 2008:chap 22.
Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; Scott Miller, MD, Urologist in private practice in Atlanta, Georgia. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.