Archives of Sexual Behavior

, Volume 41, Issue 6, pp 1507–1511 | Cite as

A Possible Second Type of Maternal–Fetal Immune Interaction Involved in Both Male and Female Homosexuality

Original Paper


Recent research has found that the mothers of firstborn homosexual sons produce fewer subsequent offspring than do the mothers of firstborn heterosexual sons. It was hypothesized that a subset of mothers of firstborn homosexuals may be responsible for this finding. If there is a subset of mothers whose immune reactions cause their first male fetus to be homosexual and their subsequent fetuses to die, then their immune reactions should also cause their first male fetus to have a lower birth weight. This leads to the prediction that, within the population of firstborn homosexual men, those with no younger siblings should also tend to have lower birth weights. This prediction was tested using a previously published sample of 1,445 firstborn subjects: 929 heterosexual females, 47 homosexual females, 409 heterosexual males, and 60 homosexual males. The results showed that firstborn homosexuals with no younger siblings (i.e., only children) did have lower birth weights compared with all the other subjects, but the finding applied to firstborn lesbian women as well as firstborn gay men.


Antibody Antigen Birth order Birth weight Fertility Heterosexuality Homosexuality Immunology Lesbian 


  1. Bailey, J. M., Dunne, M. P., & Martin, N. G. (2000). Genetic and environmental influences on sexual orientation and its correlates in an Australian twin sample. Journal of Personality and Social Psychology, 78, 524–536.PubMedCrossRefGoogle Scholar
  2. Blanchard, R. (2004). Quantitative and theoretical analyses of the relation between older brothers and homosexuality in men. Journal of Theoretical Biology, 230, 173–187.PubMedCrossRefGoogle Scholar
  3. Blanchard, R. (2008). Review and theory of handedness, birth order, and homosexuality in men. Laterality: Asymmetries of Body, Brain and Cognition, 13, 51–70.CrossRefGoogle Scholar
  4. Blanchard, R. (2011). Fertility in the mothers of firstborn homosexual and heterosexual men. Archives of Sexual Behavior. doi: 10.1007/s10508-011-9888-0.
  5. Blanchard, R., & Bogaert, A. F. (1996). Homosexuality in men and number of older brothers. American Journal of Psychiatry, 153, 27–31.PubMedGoogle Scholar
  6. Blanchard, R., & Bogaert, A. F. (2004). Proportion of homosexual men who owe their sexual orientation to fraternal birth order: An estimate based on two national probability samples. American Journal of Human Biology, 16, 151–157.PubMedCrossRefGoogle Scholar
  7. Blanchard, R., Cantor, J. M., Bogaert, A. F., Breedlove, S. M., & Ellis, L. (2006). Interaction of fraternal birth order and handedness in the development of male homosexuality. Hormones and Behavior, 49, 405–414.PubMedCrossRefGoogle Scholar
  8. Blanchard, R., & Ellis, L. (2001). Birth weight, sexual orientation and the sex of preceding siblings. Journal of Biosocial Science, 33, 451–467.PubMedCrossRefGoogle Scholar
  9. Blanchard, R., & Klassen, P. (1997). H-Y antigen and homosexuality in men. Journal of Theoretical Biology, 185, 373–378.PubMedCrossRefGoogle Scholar
  10. Blanchard, R., Zucker, K. J., Cavacas, A., Allin, S., Bradley, S. J., & Schachter, D. C. (2002). Fraternal birth order and birth weight in probably prehomosexual feminine boys. Hormones and Behavior, 41, 321–327.PubMedCrossRefGoogle Scholar
  11. Bogaert, A. F., & Skorska, M. (2011). Sexual orientation, fraternal birth order, and the maternal immune hypothesis: A review. Frontiers in Neuroendocrinology, 32, 247–254.PubMedCrossRefGoogle Scholar
  12. Cantor, J. M., Blanchard, R., Christensen, B. K., Dickey, R., Klassen, P. E., Beckstead, A. L.,… Kuban, M. E. (2004). Intelligence, memory, and handedness in pedophilia. Neuropsychology, 18, 3–14.Google Scholar
  13. Cantor, J. M., Blanchard, R., Paterson, A. D., & Bogaert, A. F. (2002). How many gay men owe their sexual orientation to fraternal birth order? Archives of Sexual Behavior, 31, 63–71.PubMedCrossRefGoogle Scholar
  14. Cantor, J. M., Klassen, P. E., Dickey, R., Christensen, B. K., Kuban, M. E., Blak, T.,… Blanchard, R. (2005). Handedness in pedophilia and hebephilia. Archives of Sexual Behavior, 34, 447–459.Google Scholar
  15. Cantor, J. M., Kuban, M. E., Blak, T., Klassen, P. E., Dickey, R., & Blanchard, R. (2006). Grade failure and special education placement in sexual offenders’ educational histories. Archives of Sexual Behavior, 35, 743–751.PubMedCrossRefGoogle Scholar
  16. Cantor, J. M., Kuban, M. E., Blak, T., Klassen, P. E., Dickey, R., & Blanchard, R. (2007). Physical height in pedophilic and hebephilic sexual offenders. Sexual Abuse: A Journal of Research and Treatment, 19, 395–407.Google Scholar
  17. Christiansen, O. B., Pedersen, B., Nielsen, H. S., & Andersen, A.-M. N. (2004). Impact of the sex of first child on the prognosis in secondary recurrent miscarriage. Human Reproduction, 19, 2946–2951.PubMedCrossRefGoogle Scholar
  18. Ellis, L., & Blanchard, R. (2001). Birth order, sibling sex ratio, and maternal miscarriages in homosexual and heterosexual men and women. Personality and Individual Differences, 30, 543–552.CrossRefGoogle Scholar
  19. Gómez-Gil, E., Esteva, I., Carrasco, R., Cruz Almaraz, M., Pasaro, E., Salamero, M., & Guillamon, A. (2011). Birth order and ratio of brothers to sisters in Spanish transsexuals. Archives of Sexual Behavior, 40, 505–510.Google Scholar
  20. Nielsen, H. S., Andersen, A.-M. N., Kolte, A. M., & Christiansen, O. B. (2008a). A firstborn boy is suggestive of a strong prognostic factor in secondary recurrent miscarriage: A confirmatory study. Fertility and Sterility, 89, 907–911.PubMedCrossRefGoogle Scholar
  21. Nielsen, H. S., Mortensen, L., Nygaard, U., Schnor, O., Christiansen, O. B., & Andersen, A.-M. N. (2008b). Brothers and reduction of the birth weight of later-born siblings. American Journal of Epidemiology, 167, 480–484.PubMedCrossRefGoogle Scholar
  22. Nielsen, H. S., Steffensen, R., Lund, M., Egestad, L., Mortensen, L. H., Andersen, A.-M. N.,… Christiansen, O. B. (2010a). Frequency and impact of obstetric complications prior and subsequent to unexplained secondary recurrent miscarriage. Human Reproduction, 25, 1543–1552.Google Scholar
  23. Nielsen, H. S., Steffensen, R., Varming, K., van Halteren, A. G. S., Spierings, E., Ryder, L. P.,… Christiansen, O. B. (2009). Association of HY-restricting HLA class II alleles with pregnancy outcome in patients with recurrent miscarriage subsequent to a firstborn boy. Human Molecular Genetics, 18, 1684–1691.Google Scholar
  24. Nielsen, H. S., Witvliet, M. D., Steffensen, R., Haasnoot, G. W., Goulmy, E., Christiansen, O. B., et al. (2010b). The presence of HLA-antibodies in recurrent miscarriage patients is associated with a reduced chance of a live birth. Journal of Reproductive Immunology, 87, 67–73.PubMedCrossRefGoogle Scholar
  25. Nielsen, H. S., Wu, F., Aghai, Z., Steffensen, R., van Halteren, A. G., Spierings, E.,… Goulmy, E. (2010c). H-Y antibody titers are increased in unexplained secondary recurrent miscarriage patients and associated with low male : female ratio in subsequent live births. Human Reproduction, 25, 2745–2752.Google Scholar
  26. Schagen, S. E. E., Delemarre-van de Waal, H. A., Blanchard, R., & Cohen-Kettenis, P. T. (2011). Sibling sex ratio and birth order in early-onset gender dysphoric adolescents. Archives of Sexual Behavior. doi: 10.1007/s10508-011-9777-6.
  27. Schwartz, G., Kim, R. M., Kolundzija, A. B., Rieger, G., & Sanders, A. R. (2010). Biodemographic and physical correlates of sexual orientation in men. Archives of Sexual Behavior, 39, 93–109.PubMedCrossRefGoogle Scholar
  28. VanderLaan, D. P., & Vasey, P. L. (2011). Male sexual orientation in Independent Samoa: Evidence for fraternal birth order and maternal fecundity effects. Archives of Sexual Behavior, 40, 495–503.PubMedCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  1. 1.Department of PsychiatryUniversity of TorontoTorontoCanada

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