Is maternal periconceptional smoking associated with 2D:4D digit ratio in their children? (Lay summary)

Velez MP, Arbuckle TE, Monnier P, Fraser WD. Journal of Developmental Origins of Health and Disease. 2017 Oct;8(5):597-603. doi: 10.1017/S2040174417000320.

The fetus is more sensitive to the toxicity of chemicals than an adult.  Smoking during pregnancy has been associated with a number of adverse health outcomes including lower fertility in the children of smoking mothers.  Some researchers have suggested that the ratio of the length of 2nd (index) and 4th (ring) fingers (2D:4D) may be an indicator of fetal concentrations of androgens (the hormones that influence development of the male reproductive system).   Males and females tend to have different 2D:4D ratios, with males tending to have shorter 2nd than 4th digit lengths.     The adverse effect of maternal smoking on their child’s later fertility may act by disturbing levels of fetal androgens.   If 2D:4D is an indicator of fetal concentrations of androgens, then 2D:4D should differ among children whose mothers smoked during the pregnancy compared with those whose mothers did not smoke.  The MIREC Study was used to test this theory.

Information on smoking before and during pregnancy was collected by questionnaire.  As part of the MIREC-CD Plus Study, the lengths of the 2nd and 4th fingers were measured in 749 children. The results showed that approximately 12% of the women reported smoking during the 1st trimester or 1 year before the pregnancy.  Boys had lower 2D:4Ds compared with girls. The average 2D:4D among children whose mothers had smoked was not different than among those whose mothers did not smoke,  The only factors that were associated with the child’s 2D:4D were their age and their mother’s 2D:4D ratios.  In conclusion, the 2D:4D ratio may not be a good indicator of androgen levels in the fetus.

Although the number of women who smoked in this study was low, the study did not find an association between mother’s smoking and their child’s 2D:4D ratios.