57. Time-to-pregnancy and offspring finger-length ratio (2D:4D) (lay summary)

Shere M, Arbuckle TE, Monnier P, Fraser WD, Velez MP. American Journal of Human Biology. 2018 Oct 17:e23176. doi: 10.1002/ajhb.23176.

Several different indicators have been proposed to assess the potential reproductive toxicity of hormone-disrupting chemicals. One potential indicator is the ratio of the lengths of the 2nd and 4th fingers (2D:4D). Some researchers think that a person’s 2D:4D ratio is a marker of greater exposure to the male hormone androgen during fetal development as boys tend to have lower 2D:4D ratios than girls. Another, more common indicator of potential reproductive toxicity is the number of months it takes for a couple to get pregnant (time to pregnancy). A longer time to pregnancy is a measure of the couple’s fertility. This study was done to see if the 2D:4D ratio for MIREC kids was different if it took their parents longer to get pregnancy.

Women in the study were asked the number of months it took them to get pregnant with the current pregnancy. Digital photographs of both hands were taken to calculate 2D:4D for the woman and her child (at 2-5 years of age). Various statistical techniques were used to study the association between time to pregnancy, or use of assisted reproductive technologies (ART), and the child’s 2D:4D ratio.

Data from 673 mother-child pairs from the MIREC Study were analysed. The results showed that boys had significantly lower 2D:4D compared to girls, but that there was no association between 2D:4D and time to pregnancy or any measure of fertility. The only factors associated with the child’s 2D:4D were the child’s age and the woman’s 2D:4D.

In conclusion, this study found that boys had lower 2D:4D ratios than girls, which agrees with other studies. However, the results suggest that there is no association between 2D:4D ratios and the couple’s fertility and therefore 2D:4D ratios may not be a good indicator of potential reproductive toxicity of various chemicals.