Testing the twin testosterone transfer hypothesis: Intergenerational analysis of 317 dizygotic twins born in Aberdeen, Scotland

Chiara Talia, Edwin-Amalraj Raja, Sohinee Bhattacharya, Paul A. Fowler *

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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STUDY QUESTION: Does having a male co-twin influence the female twin’s reproductive outcomes?
SUMMARY ANSWER: Women with a male co-twin had the same chances of being pregnant and having children compared to samesex twin pairs.
WHAT IS KNOWN ALREADY: According to the twin testosterone transfer (TTT) hypothesis, in an opposite-sex twin pregnancy, testosterone transfer from the male to the female co-twin occurs. A large body of literature supports the negative impact of prenatal testosterone exposure on female’s reproductive health in animal models; however, evidence from human studies remains controversial.
STUDY DESIGN, SIZE, DURATION: This cohort study included all dizygotic female twins in the Aberdeen Maternity and Neonatal
Databank (Scotland) born before 1 January 1979. The 317 eligible women were followed up for 40 years for any pregnancies and the outcome of those pregnancies recorded in the same database.
PARTICIPANTS/MATERIALS, SETTING, METHODS: Fertility outcomes (number of pregnancies, number of livebirths and age at first pregnancy) were compared between women with a male co-twin (exposed group, n ¼ 151) and those with a female co-twin (unexposed group, n ¼ 166). Population averaged models were used to estimate odds ratios (OR) and 95% CI for all outcomes with adjusting
for potential confounders.
MAIN RESULTS AND THE ROLE OF CHANCE: There were no differences in chances of having pregnancies (adj. OR 1.33; 95% CI 0.72, 2.45) and livebirths (adj. OR 1.22; 95% CI 0.68, 2.18) between women from same-sex and opposite-sex twin pairs. Women with a male co-twin were more likely to smoke during pregnancy and, in the unadjusted model, were younger at their first pregnancy (OR 2.13; 95% CI 1.21, 3.75). After adjusting for confounding variables (year of birth and smoking status) the latter finding was no longer significant
(OR 1.67; 95% CI 0.90, 3.20).
LIMITATIONS, REASONS FOR CAUTION: The dataset was relatively small. For women without a pregnancy recorded in the databank, we assumed that they had not been pregnant.
WIDER IMPLICATIONS OF THE FINDINGS: Despite the evidence from animal studies concerning the adverse effects of prenatal
testosterone exposure on female health, our results do not support the TTT hypothesis. The finding that women with a male co-twin are more likely to smoke during pregnancy highlights the importance of considering post-socialisation and social effects in twin studies.
STUDY FUNDING/COMPETING INTEREST(S): European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie project PROTECTED (grant agreement No. 722634) and FREIA project (grant agreement No. 825100). No competing interests.
Original languageEnglish
Pages (from-to)1702-1710
Number of pages9
JournalHuman Reproduction
Issue number7
Early online date19 Jun 2020
Publication statusPublished - 31 Jul 2020

Bibliographical note

The authors would like to apologise for errors in Table IV and Supplementary Table SI of the above article.

The authors thank the custodians of Aberdeen Maternal and Neonatal Databank for granting access to the required dataset.

This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 722634.


  • twin
  • testosterone transfer
  • fertility
  • prenatal androgen exposure
  • reproductive history
  • Twin
  • Reproductive history
  • Fertility
  • Testosterone transfer
  • Prenatal androgen exposure


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