Iam a 28 years old veterinarian, iam pregnant (12 weeks fetus), i have an orange sized simple cyst on my left ovary. what is your advice?

Watch/wait: Most doctors would watch and wait for something that would compell them to act.

Wait and see: Follow with ultrasoiund unless symptomatic or suspicious on ultrasound, oranges come in different sizes, how many entimeters?

Here are some...: Based on what described, I assumed you're in the first pregnancy and the "orange-sized' left ovarian simple cyst is an incidental finding. Although the most reasonable course of care is focus on fetal nurturing, care, and F/U, still ask and work with the attending doc for individual details on the related subjects so to balance between medical necessities and professional possibilities.