Twenty week old foetus. Coloured ultrasound scan of a 20 week (five month) old human foetus in side view. The head is at right, seen in profile facing upwards. The torso is at lower centre with vertebrae of the spine seen. A hand is visible above the torso, and a leg is at left. The crown- rump length (sitting height) of a foetus at 20 weeks is about 19 centimetres and its weight about 450 grams. Growth in length is particularly striking during the 3rd, 4th and 5th months. The foetus is covered with fine hair, called lanugo; eyebrows and head hair have also developed, and movements of the foetus are felt by the mother.