Selenium is teratogenic in high quantities – its presence in the diet or tissues of a pregnant female can cause abnormalities in the offspring. Studies into tissue selenium residues in fish populations have shown an exponential relationship between selenium levels and teratogenic defects - however this was only noted in one isolated population.
Defects include curvature of the spine, head deformities, cataracts, edema, and gross deformities such as missing eyes and missing or shortened limbs - think of the thalidomide babies – thalidomide is also teratogenic. However, no studies have demonstrated that selenium is teratogenic in humans – anecdotal reports suggest that it is, but I could find no evidence to lend weight to these suggestions. Excess selenium has been demonstrated to be teratogenic in birds, producing deformities such as those listed above.
Acknowledgements:
http://www.ithyroid.com/selenium.htm
http://www.womensdoctor.com/Vitamins%20and%20Minerals.htm
http://www.atsdr.cdc.gov/toxprofiles/tp92-c3.pdf