Twins and prenatal testosterone exposure

A study explores the long-term effects of prenatal exposure of human female co-twins to testosterone derived from male co-twins. In litter-producing species, such as rats and guinea pigs, female littermates exposed to testosterone derived from male littermates inside the uterus have been known to exhibit male-typical morphological and behavioral traits as adults. To uncover potential long-term effects of such prenatal testosterone exposure on human female co-twins, Aline Bütikofer, David N. Figlio, Krzysztof Karbownik, Christopher W. Kuzawa, and Kjell G. Salvanes analyzed birth, household composition, schooling, and employment data for more than 13,700 twins born in Norway between 1967 and 1978. Compared with female co-twins not exposed to a male co-twin inside the uterus, female co-twins exposed to a male co-twin had 15.2% higher probability of dropping out of high school, 11.7% lower probability of ever having been married by age 32, 8.6% lower earnings at age 32, and 5.8% fewer children. To rule out possible postnatal effects of being raised with a male co-twin, the authors included data on subsets of female co-twins whose male co-twin died after the first 28 days or the first year of life. The latter analysis suggested that the observed association was likely due to prenatal testosterone exposure rather than postnatal effects. The authors also ruled out a role for potential prenatal nutritional disadvantages faced by female co-twins. Thus, in utero testosterone transfer may have lasting effects on female children. The findings are salient given the increasing rate of twin births in Brazil, China, Europe, and North America, paralleled by delayed childbirth and growing use of assisted reproductive technologies, according to the authors.

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Article #18-12786: "Evidence that prenatal testosterone transfer from male twins reduces the fertility and socioeconomic success of their female co-twins," by Aline Bütikofer, David N. Figlio, Krzysztof Karbownik, Christopher W. Kuzawa, and Kjell G. Salvanes.

MEDIA CONTACT: Krzysztof Karbownik, Emory University, Atlanta, GA; tel: 224-235-5870; e-mail: krzysztof.karbownik@emory.edu