When a solid turns into a liquid it is called fusion, more commonly referred to as melting. When a material moves from one state of matter into another it is called a phase transition. Fusion is just...
Human pregnancy can be divided roughly into three trimesters, each approximately three months long. The first trimester is from the last period to the 13th week, the second trimester is from the 14th to 27th week, and the third trimester is from the 28th week to the 42nd week. In humans, birth normally occurs at a gestational age of about 40 weeks, though it is common for births to occur from 37 to 42 weeks.
This photo shows a baby at 16 weeks of gestation during the second trimester of pregnancy. At this stage: Tissues including bones and muscles continue to form. The baby begins to develop translucent skin. The baby begins to form a substance called meconium, which is the first bowel movement.