Archives of Sexual Behavior

, Volume 40, Issue 3, pp 505–510 | Cite as

Birth Order and Ratio of Brothers to Sisters in Spanish Transsexuals

  • Esther Gómez-GilEmail author
  • Isabel Esteva
  • Rocío Carrasco
  • M. Cruz Almaraz
  • Eduardo Pasaro
  • Manel Salamero
  • Antonio Guillamon
Original Paper


Three Western studies have shown that male-to-female (MF) homosexual transsexuals tend to be born later than their siblings and to come from sibships with more brothers than sisters. The objective of this study was to determine whether these variables would be replicated in 530 MF and female-to-male (FM) Spanish transsexuals according to sexual orientation. The results showed that MF homosexual transsexuals had significantly more older brothers than the non-homosexual MF group. Compared with the expected rates in the general population, birth order was significantly higher in both MF (Slater’s Index = 0.59; Fraternal Index = 0.61; Sororal Index = 0.58) and FM homosexual transsexuals (Slater’s Index = 0.65; Fraternal Index = 0.68; Sororal Index = 0.67), and sibling sex ratio was significantly higher than expected in homosexual MF (sex ratio = 0.55) but not in homosexual FM transsexuals. No significant differences were found in the non-homosexual subgroups. The replication of the later birth order and sibling sex-ratio effect in MF homosexual transsexuals corroborates previous findings in a variety of groups from different cultures and may suggest a common mechanism underlying the etiology of transsexualism.


Birth order Sibling sex ratio Gender identity disorder Transsexualism Sexual orientation 



This research was supported by grants SEJ2007-65686/PSIC, PI-0254/2007 JA, and MIG 238/2009.


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Copyright information

© Springer Science+Business Media, LLC 2010

Authors and Affiliations

  • Esther Gómez-Gil
    • 1
    • 6
    Email author
  • Isabel Esteva
    • 2
  • Rocío Carrasco
    • 3
  • M. Cruz Almaraz
    • 2
  • Eduardo Pasaro
    • 4
  • Manel Salamero
    • 1
  • Antonio Guillamon
    • 5
  1. 1.Unidad de Identidad de Género, Instituto Clínic de Neurociencias, Servicio de Psiquiatría, Hospital ClínicUniversidad de BarcelonaBarcelonaSpain
  2. 2.Unidad de Trastornos de Identidad de Género, Servicio de EndocrinologíaHospital Carlos HayaMálagaSpain
  3. 3.Unidad de Trastornos de Identidad de Género, Servicio de GinecologíaHospital Carlos HayaMálagaSpain
  4. 4.Departamento de PsicobiologíaUniversidad de A CoruñaA CoruñaSpain
  5. 5.Departamento de PsicobiologíaUNEDMadridSpain
  6. 6.Department of Psychiatry, Institute Clinic of Neurosciences, Hospital ClínicUniversity of BarcelonaBarcelonaSpain

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