Trimester 1- Flesh and tissue coming together. Trimester 2- Lungs and heart forming. Trimester 3- The baby gains weight. A misscarrage is when the baby doesnt attach to the uterine wall before it can survive on its own. A stillbirth is the death of a viable baby in the womb or as its being birthed. Gestational diabetes and placenta accreta can both happen during pregnancy.