Birth weight and two possible types of maternal effects on male sexual orientation: A clinical study of children and adolescents referred to a Gender Identity Service

Abstract

This study tested predictions regarding two hypothesized maternal immune responses influencing sexual orientation: one affecting homosexual males with high fraternal birth order and another affecting firstborn homosexual individuals whose mothers experience repeated miscarriage after the birth of the first child. Low birth weight was treated as a marker of possible exposure to a maternal immune response during gestation. Birth weight was examined relative to sibship characteristics in a clinical sample of youth (N = 1,722) classified as heterosexual or homosexual based on self-reported or probable sexual orientation. No female sexual orientation differences in birth weight were found. Homosexual, compared to heterosexual, males showed lower birth weight if they had one or more older brothers--and especially two or more older brothers--or if they were an only-child. These findings support the existence of two maternal immune responses influencing male sexual orientation and possibly also cross-gender behavior and identity.

Towards a further understanding of prenatal thyroid theory of homosexuality: Autoimmune thyroiditis, polycystic ovary syndrome, autism and low birth weight

“…Many studies have investigated associations among birth weight, sexual orientation and sibship status, [31][32][33] and some mildly significant results for males have been reported. It is hypothesized that the maternal immune reaction against the male fetus may adversely affect specific brain areas associated with typical sexual orientation, and this effect may correlate with the degree of fetal growth retardation.…”

“…It is hypothesized that the maternal immune reaction against the male fetus may adversely affect specific brain areas associated with typical sexual orientation, and this effect may correlate with the degree of fetal growth retardation. [31][32][33] In a recent study, a distinct type of maternal immune response implicated in the etiology of male sexual orientation was investigated, with low birth weight and high fetal loss used as markers. 34 Like those of previous indirect measures of research used in the study of sexual orientation, low birth weight and high fetal loss are neither specific nor sensitive enough to be employed as markers.…”

Testosterone, Fraternal Birth Order, and Homosexuality: Comment on Kishida and Rahman (2015)

“…It was reported that homosexual, compared to heterosexual, males showed lower birth weight, especially if they had two or more older brothers. The increased maternal inflammatory state, as a consequence of previous pregnancies, might therefore have contributed both to the homosexual orientation and to the low birth weight (VanderLaan, Blanchard, Wood, Garzon, & Zucker, 2015).…”

O Gay New World: Ramifications of the Maternal Immune Hypothesis

“…A distinct maternal immune response may also affect some gay men who are only-children; mothers of gay male only-children report a higher rate of miscarriage, and firstborn gay male only-children have a lower birth weight compared to: (1) firstborn heterosexual male only-children, (2) heterosexual males with siblings, and (3) gay males with older brothers (Skorska, Blanchard, VanderLaan, Zucker, & Bogaert, 2017;VanderLaan et al, 2015).…”

“…Although the putative male-specific antigen or antigens are unknown at this time, candidate antigens and maternal antibodies have been proposed (e.g., Bogaert & Skorska, 2011;VanderLaan et al, 2015), and perhaps it is only a matter of time before these antibodies are discovered. If a specific antigen is discovered to mediate the FBOE, then shielding the mother's immune system from exposure to the antigen should eliminate the FBOE.…”