Ultrasound scan of a human foetus at 20 weeks showing head (centre right) and abdomen (centre). At this stage the foetus measures about 20 centimetres and weighs around 500 grams and has fully developed organs, limbs, fingers and toes. This image has been taken using ultrasound scanning. This technique involves the passing of high frequency sounds through the mother's abdomen using a transducer. The echoes are recorded to build up a picture of the foetus. It is a useful way to monitor and examine the health and growth of the foetus.