Pregnant (adj) = having a child or other offspring developing in the body; with child or young, as a woman or female mammal: Pregnant | Define Pregnant at Dictionary.com

Pregnant (adj) = carrying a fetus or fetuses within the womb: pregnant definition | English definition dictionary | Reverso Collins

In biology, the term gravid is used to describe the condition of an animal (most commonly fish or reptiles) when carrying eggs internally.

In medicine, pregnancy is often defined as beginning when the developing embryo becomes implanted in the endometrial lining of a woman's uterus. Merely having a fertilized egg inside of her isn't enough to define her as "pregnant"

Now, I do realize that "gravid" is simply a Latin word for "heavy", but "pregnant" as I have always understood, is not the correct term for an animal that is simply carrying eggs, even if those eggs are developing within the body, as is the case with garter snakes.

You can call a woman "gravid" and still be correct, but to call a snake "pregnant" is not correct. That's what I've always been taught, and that is how I've always understood it. You wouldn't call a chicken about to lay an egg "pregnant" now would you? In any biology class I've ever taken, you would quickly be corrected if you called a snake, fish, or bird, "pregnant"