Months 4 through 6 of the pregnancy are called the second trimester. Most women feel more energized in this period, and begin to put on weight as the symptoms of morning sickness subside and eventually fade away.
In the 20th week the uterus, the muscular organ that holds the developing fetus, can expand up to 20 times its normal size during pregnancy.
Although the fetus begins moving and takes a recognizable human shape during the first trimester, it is not until the second trimester that movement of the fetus, often referred to as "quickening", can be felt. This typically happens in the fourth month, more specifically in the 20 to 21 week, or by the 19th week if the woman has been pregnant before. However, it is not uncommon for some women to not feel the fetus move until much later. The placenta is now fully functioning and the fetus is making insulin and urinating. The reproductive organs distinguish the fetus as male or female.