1 - Serviço de Ginecologia/Obstetrícia, Hospital Dona Estefânia, Centro Hospitalar de Lisboa Central, E.P.E.;
2 - Epidemiologia, Faculdade de Ciências, Universidade de Lisboa;
3 - Biochemestry, School of Biomedical Sciences, King's College London, Franklin Wilkins building, Waterloo, London SE1 9NH;
4 - Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Campo dos Mártires da Pátria Lisboa, Portugal
- 3º Congresso Internacional da Union of European Neonatal & Perinatal Societies (UENPS), 14 – 17/11/2012, Porto - Portugal (Poster).
- Revista Acta Médica Portuguesa 2012; 3rd International Congress of UENPS, Speakers;25(S2):148 (PO11) (Resumo).
Introduction: The 2D:4D digit ratio is sexually-dimorphic and has attracted attention because it could be an accessible anthropometric surrogate marker for prenatal androgen exposure, helping prediction of pathology and behavior later in life, and facilitating early screening of individuals at risk. We aim to examine dimorphism in the 2D:4D digit ratio at delivery (first 48 hours), a period of time in between the pre and postnatal peaks of testosterone production. We report on how the ratio of the newborn (NB) infant correlates with testosterone in maternal plasma and amniotic fluid (AF).
Subjects and Methods: Testosterone was assayed in samples of maternal plasma and AF, both collected when mothers attended amniocentesis (16-23 weeks of pregnancy). Shortly after birth, 106 mother-newborn pairs were measured for finger length and 2D:4D ratio.
Results: NB males had longer fingers and lower mean 2D:4D ratio than females. However, the difference in 2D:4D was significant only for the left hand (males: 0.927; females: 0.950; t = 2.95, p = 0.004). The 2D:4D mean ratios of NBs were lower than those of their mothers (p < 0.001) regardless of sex and hand. Testosterone in males AF was significantly higher than in females (males: 0.83 nmol/L, females: 0.34 nmol/L; p < 0.001); there was no correlation between testosterone in the AF and in the mother's plasma. Both hands of NB females were negatively correlated with AF testosterone, but not males. Maternal plasma testosterone also showed a negative weak correlation with NB digit ratio in both hands and sexes.
Conclusions: Sexual dimorphism was present at birth, indicating the effect of prenatal testosterone, but it was only significant for the left hand, in contrast with previous reports for individuals older than 2 years old, suggesting that postnatal testosterone is determinant for ratio stabilization in the right hand. Our data also supports the claim that 2D:4D increases from birth to adulthood. The association between AF testosterone and female's digit ratio, but not male's, suggests that because the male fetus is normally subjected to higher levels of testosterone, levels of above average do not have significant impact in further decreasing their 2D:4D ratio.
Keywords: Newborn, testosterone, 2D:4D, anthropometric marker.