gestational age vs fertilization age

gestational age and fertilization age both are nouns.

Word	Noun	Adjective	Verb	Adverb
gestational age	Yes	No	No	No
fertilization age	Yes	No	No	No

As nouns, gestational age and fertilization age are synonyms defined as:

gestational age and fertilization age: the age of an embryo counting from the time of fertilization

Other synonyms of gestational age include fetal age.

gestational age (noun)	fertilization age (noun)
the age of an embryo counting from the time of fertilization	the age of an embryo counting from the time of fertilization