FYI--There is no such thing as a "fertilized egg".
At fertilization the egg and sperm cease to be. They become a one celled blastocyst with the same DNA that life will have till he/she dies. Be it at 93 years or 93 minutes. At this one cell stage the sex is known, as well as all the info that can be gotten from a DNA test on you or me.
Day 1--Fertilization Check
Early in the morning, the eggs are checked for signs of fertilization. At this time, normally fertilized eggs will have 2 nuclei in the center, one from the egg and one from the sperm. (as shown below)
Any number of nuclei greater or lesser than 2 indicates abnormal fertilization. Normally fertilized eggs are now considered to be embryos, and are separated from the unfertilized and abnormally fertilized eggs.
Strong Health
I know when I took Embryology, Cellular Biology, and Comparative Anatomy the term fertilized egg was acceptable.
At fertilization the egg and sperm cease to be. They become a one celled blastocyst Better brush up on your terminology. There is no such thing a "one celled blastocyst". "Blastocyst" refers to the many-celled stage where the embryo has differentiated into two different types of cells, in two separate regions, one of which will become the placenta and the other of which will become the fetus.