Fertility clinic egg (4)
I believe the answer is:
ovum
'fertility clinic egg' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ovum that I've seen before include "Reproductive cell, 'egg' in Latin" , "bit of life potentially" , "Human egg cell" , "A female egg-cell" , "Female reproductive cell" .)