File:Human fetus skeleton x-ray 01.jpg

Figure 1. Examples of fetuses that should be excluded and included from FA measurements.

A: Fetus with limb deformities (indicated by arrows), which include bowing of the radius and ulna, bowing of the digits, bowing and hypoplasia of the femur, tibia and fibula. B: Fetus with limb deformities including bowing of the digits, bowing and hypoplasia of the femur, tibia and fibula, and talipes equinovarus (clubfeet). The deformed traits in fetus A and B should be excluded from FA measurements. C: Non-deformed, representative fetus, that allows FA measurements: the limbs are properly positioned and no deformities are present. Here, fetuses A and B developed with reduced amniotic fluid volumes and fetus C developed with a normal amniotic fluid volume. doi:10.1371/journal.pone.0081824.g001

PLoS One. 2013 Nov 27;8(11):e81824. doi: 10.1371/journal.pone.0081824. eCollection 2013. Amniotic fluid deficiency and congenital abnormalities both influence fluctuating asymmetry in developing limbs of human deceased fetuses. ten Broek CM1, Bots J, Varela-Lasheras I, Bugiani M, Galis F, Van Dongen S. Author information

Abstract Fluctuating asymmetry (FA), as an indirect measure of developmental instability (DI), has been intensively studied for associations with stress and fitness. Patterns, however, appear heterogeneous and the underlying causes remain largely unknown. One aspect that has received relatively little attention in the literature is the consequence of direct mechanical effects on asymmetries. The crucial prerequisite for FA to reflect DI is that environmental conditions on both sides should be identical. This condition may be violated during early human development if amniotic fluid volume is deficient, as the resulting mechanical pressures may increase asymmetries. Indeed, we showed that limb bones of deceased human fetuses exhibited increased asymmetry, when there was not sufficient amniotic fluid (and, thus, space) in the uterine cavity. As amniotic fluid deficiency is known to cause substantial asymmetries and abnormal limb development, these subtle asymmetries are probably at least in part caused by the mechanical pressures. On the other hand, deficiencies in amniotic fluid volume are known to be associated with other congenital abnormalities that may disturb DI. More specifically, urogenital abnormalities can directly affect/reduce amniotic fluid volume. We disentangled the direct mechanical effects on FA from the indirect effects of urogenital abnormalities, the latter presumably representing DI. We discovered that both factors contributed significantly to the increase in FA. However, the direct mechanical effect of uterine pressure, albeit statistically significant, appeared less important than the effects of urogenital abnormalities, with an effect size only two-third as large. We, thus, conclude that correcting for the relevant direct factors allowed for a representative test of the association between DI and stress, and confirmed that fetuses form a suitable model system to increase our understanding in patterns of FA and symmetry development.

Reference

<pubmed>24312362</pubmed> PLoS One.

Copyright

© 2013 ten Broek et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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