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.
The first trimester is week 1 through to the end of week 13. The second trimester usually ends around the 26th week and consists of the 4th, 5th and 6th completed months. The third trimester can end anywhere between the 38th - 42nd week and is the 7th, 8th and 9th completed months of pregnancy.