Does a baby breathe in the uterus beforehand being born?

No

Explanation:

Because Babies lungs do not function the same way in the womb as they do outside of the womb. Before birth a baby's lungs are filled with amniotic fluid. They do “practice” breathing towards the end of the pregnancy with periodic inhaling and exhaling of amniotic fluid.

starvation is bad because your body needs nutrition and to deprive it of nutrition can cause problems with both health and fitness.

explanation:

it can make weight loss slow down over time, but it won't cause someone to gain weight depsite restricting calories. starvation causes weakness in the senses like thirst.