fetal age vs gestational age

fetal age and gestational age both are nouns.

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

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

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

Other synonyms of fetal age include fertilization age.

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