Female digit length ratio (2D:4D) and time-to-pregnancy (Lay summary)

Vélez MP, Arbuckle TE, Monnier P, Fraser WD. Human Reproduction. 2016 Sep;31(9):2128-34. doi: 10.1093/humrep/dew164. 

Some environmental chemicals may affect the body’s hormones, including those involved in fertility and reproductive health.  To aid in determining if specific chemicals are hormone-disrupting, it would be useful to have a reliable hormone-sensitive health endpoint as a marker of a potential effect.  The ratio of the lengths of the 2nd (index) and 4th (ring) fingers (2D:4D) has been proposed as a potential marker of greater exposure to androgens during fetal development.  Males tend to have shorter 2D:4D than females.  Androgens are hormones that primarily influence the male reproductive system.  It has been suggested that variations in androgen levels during fetal development may be expressed as differences in 2D:4D between people of the same sex and effects on fertility.  One way to measure a couple’s degree of fertility is to ask how many months of trying it took to become pregnant (time-to-pregnancy) (TTP).  This study was designed to see if there is any association between the woman’s finger digit length ratio (2D:4D) and time to pregnancy with the MIREC child.

As part of the MIREC follow-up study, MIREC-CD Plus, MIREC staff took digital pictures of each of the women’s hands.  Using these pictures, staff measured the length of the 2nd and 4th fingers of each hand and calculated the finger digit ratios for each hand (2D:4D).  Approximately 700 women from 6 Canadian cities participated. Information on how long the couple took to get pregnant was collected in the MIREC questionnaire and compared to the 2D:4D.

No association was found between the woman’s 2D:4D and how long it took the couple to become pregnant. However, there were some limitations with this study.  As MIREC was designed to conduct research on pregnant women, it naturally excluded women (or couples) who were infertile and therefore it is unknown whether infertile women might have different finger digit length ratios.  In conclusion, the results of this study do not support an association between maternal 2D:4D and time-to-pregnancy. The use of the 2D:4D as a reproductive endocrine-sensitive endpoint needs to be further evaluated before it can be recommended as a good predictor.