See below. Average fetus at 20 weeks weighs about 1 lb and 8.5 inches long. Major internal organs are all formed, external details of face, genitalia, and extremities have developed. Skin is very thin and cartilage has not formed well yet. Fetus of 20 weeks cannot survive outside womb since effective breathing and gas exchange mechanism has not developed yet.
Almost like infant. Since human gestation is 40 weeks long, 20 weeks would mark the half-way point in your pregnancy and believe it or not, your baby will look very identifiably like an infant! this is why an ultrasound is performed at around this time (structural survey), where body structures and vital organs are viewed to make sure your baby is growing/developing appropriately. The gender can also be determined.