What is the proper term for when an animal is "pregnant" with eggs instead of live young?

gravid

/ˈɡravɪd/

adjective

adjective: gravid

1.

technical carrying eggs or young; pregnant. "the retroverted gravid uterus"

Oxford Dictionaries

in lay (entry 'lay' section phrases
(of a hen) laying eggs regularly.

http://www.oxforddictionaries.com/definition/english/lay

Definition of gravid in English: adjective 1 technical Carrying eggs or young; pregnant: the retroverted gravid uterus

http://www.oxforddictionaries.com/definition/english/gravid

From the oxford dictionary:

oviparous - producing young by means of eggs that are hatched after they have been laid by the parent

viviparous bringing forth live young that have developed inside the body of the parent

Although it doesn't especially refer to fish, birds, or the like, the French loanword enceinte is quite useful.

enceinte. (n.d.) Random House Kernerman Webster’s College Dictionary. (2010). Retrieved August 18 2015 from http://www.thefreedictionary.com/enceinte

Its probable etymology from Latin incincta "ungirded" alludes to the gravid female's preparation for imminent parturition.

Gravid always works, for pregnant mammals,reptiles, birds, fish...any creature that bears young. It is well-understood by veterinarians and lay-people. It does not come with the "human-only" baggage that "pregnant" does.