Anthropometric measures do not explain the 2D:4D ratio sexual dimorphism in 7‐year‐old children

Abstract

Objectives Digit ratio (2D:4D) might reflect prenatal testosterone exposure and has been used as a putative marker for androgen related outcomes. However, such associations might be inflicted by confounders. Application of 2D:4D in epidemiological research motivate identification of biological background determinants. We examined sex, anthropometric measures, and maternal factors as determinants of 2D:4D in Swedish 7‐year‐old children. Methods The study was embedded in the Swedish Environmental, Longitudinal, Mother and Child, Asthma and Allergy (SELMA) pregnancy cohort. A total of 870 pre‐pubertal children, median 7.5 years of age, were studied. A single assessor performed digit measurements from scanned photocopies using computer software. Child anthropometric measurements investigated were hand size, birthweight, recumbent birth length, standing height, weight, BMI, body fat percentage, and waist/hip circumference. Maternal factors included age, pregnancy length, parity, and education. Results We found a significant sexual dimorphism regarding digit lengths and 2D:4D, boys on average presenting a lower 2D:4D than girls also after adjustment for summed finger lengths and body fatness. In crude analyses, maternal age correlated with 2D:4D across the whole population and in females but not in adjusted models. No other study variables were associated with 2D:4D. Conclusion Digit ratio showed sexual dimorphism at the age of seven and seems to represent a true sex difference rather than an artifact and bias from hand size, body size or body fat content. Among the rest of our investigated variables, we found no determinants constituting important confounders in future research on 2D:4D ratio.

Investigating the ratio between the lengths of the second and fourth fingers in newborns: its relationship with the umbilical cord testosterone level at Shahidan-e-Mobini hospital during the year 2021

“…they reported that the ratio was shorter in boys than girls (24). The results of another study showed that the 2D:4D ratio is signi cantly different in the two sexes and is shorter in boys than in girls (25). Malas et al showed no statistically signi cant difference between boys and girls in terms of this ratio (26), which is consistent with the results of the present study.…”

Associations of CAG repeat polymorphism in the androgen receptor gene with steroid hormone levels and anthropometrics among men: the role of the ethnic factor

“…These data confirm the hypothesis of sexual dimorphism with respect to the 2D:4D ratio, which reflects the levels of embryonic sex steroids. Sexual dimorphism in relation to the 2D:4D ratio persists throughout life, although data concerning sexual differences in this ratio in childhood are less variable compared to data in adults (Knickmeyer et al, 2011;Mitsui et al, 2015;Jägetoft et al, 2022).…”

“…The ratio between length of the index and ring digit (2D:4D) has therefore been proposed to serve as a proxy marker for in utero androgen exposure. Several reviews and meta-analyses have shown that in most cases men and boys have lower values of this ratio than women and girls, suggesting that the gender difference in the 2D:4D ratio is determined by higher levels of androgens in male embryos compared to female (Hönekopp et al, 2007;Grimbos et al, 2010;Knickmeyer et al, 2011;Xu, Zheng, 2015;Swift-Gallant et al, 2020;Jägetoft et al, 2022). One study (Mitsui et al, 2015) showed gender differences in testosterone levels of umbilical cord blood samples, which were significantly higher in samples collected from males than those from females.…”

No association between developmental instability as a general measure of stress and2D:4Ddigit ratios in a non‐western sample

“…Another criticism towards ratios and 2D:4D in particular is that sexual dimorphism in 2D:4D might have aroused because of the basically size differences between two sexes. It is thought that sexual dimorphism in 2D:4D is mainly caused by the shift along the common allometric line (Kratochvíl & Flegr, 2009; but see Jägetoft et al, 2022). Van Dongen (2009) in his study revealed that the use of digit length as both dependent and independent variables can result in artificial correlations in FA studies.…”