The major organ systems are formed, the circulatory and urinary systems are operating, and the fetus weighs about a half ounce. What stage of pregnancy is described?

First Trimester stage of Pregnancy

Explanation:

The first 3 months of pregnancy is called the First Trimester.

This stage is the most critical stage as there is a lesser chance of miscarriage after getting past this stage and the major organ system are formed. The baby's brain isn't fully developed yet and the sex is still unknown at this stage. The baby also weighs less due to the underdevelopment.