Stage 1, Unfertilized.
A. Single cell, unfertilized ovum (UFO) which may be collected on Day 7 from a superovulated donor along with embryos. The perivitelline membrane is intact and smooth. It is sometimes called a teddy bear eye. Comment: fertilization failure may be the result of asynchronous insemination, or insemination with dead or poor quality spermatozoa. B. Single cell, unfertilized oocyte in which the degenerated cellular material has pulled away from the vitelline membrane. It is sometimes referred to as a pseudoblastocyst which it may resemble when slightly out of focus or when the lenses are dirty. The contour of the vitelline membrane is smooth. C. Unfertilized ovum that has started to degenerate giving it a granular appearance. It is sometimes referred to as a salt and pepper egg.
Wright JM (2004)