Analysis of Ratio of Length of 2nd Digit to 4th Digit (2D:4D) among Transgender Women (MtF) and Cisgender People in South Indian Population: A Cross-sectional Study

Abstract

Introduction: Transgender refers to an individual whose gender identity differs from the sex that was assigned at birth. Transgender women (MtF) were assigned male at birth but later recognised themselves as female. The length of the index finger (2D) in males is shorter than the length of the ring finger (4D), resulting in a low finger ratio due to higher androgen levels, whereas in females, the ratio is high due to low androgen levels. The index to ring finger length ratio in males and females is influenced by testosterone hormone levels during early foetal life, exhibiting sexual dimorphism. The 2D:4D ratio serves as one of the determinants for future generations to identify the transgender women population. Aim: To determine the 2D:4D ratio among transgender women and the cisgender population. Materials and Methods: A cross-sectional study was conducted in the Department of Anatomy, Annapoorana Medical College and Hospitals, Vinayaka Mission’s Medical College Hospitals, Salem, Tamil Nadu, India, from September 2018 to October 2019. A total of 392 adult participants between 19 years and 60 years of age were selected. The samples of transwomen were collected with the help of the President of Salem Thirunangaigal Nala Sangam (STNS) and Koovagam Koothandavar Temple in Tamil Nadu. Cisgender samples were collected from volunteers in Salem, Tamil Nadu. The 2D and 4D digit lengths of both hands were measured using Digimizer software with the help of images obtained by a Canon 220 photo scanner. Another type of classification was done by naked eye analysis without any calculations, based on which the 2D:4D ratio among males, females and transgender women was categorised into types 1, 2 and 3. The paired t-test was used to compare the male, female and transwomen populations. Results: Out of 392 participants, 122 were cis females, 130 were cis males and 140 were transgender females. The p-value of the mean 2D:4D ratio was found to be significant in the right and left hands when comparing the 2D:4D ratio of males with females and transgender women with females. The p-value of the 2D:4D ratio for males with transgender women in the right and left hands was 0.451 and 0.943, respectively, which was statistically insignificant due to the high levels of androgen in these two groups. Conclusion: The present study helps scientists in the gender study field to advance their knowledge about transgender individuals, which can fill the gaps in available information and overcome existing lacunae in this field.

Keywords

• androgen
• digit ratio
• index finger
• sexual dimorphism