IUD contraceptive. Coloured ultrasound scan of the uterus of a woman, showing a fitted intrauterine contraceptive device (IUD, bright orange, centre) or coil. It comprises a T-shaped piece of plastic or metal that is inserted through the cervix into the womb to prevent pregnancy. It is thought to work by inhibiting the implantation of a fertilised egg. Some IUD's contain a progestogen drug that suppresses ovulation. IUD's are not as effective as the pill. Ultrasound is a diagnostic technique that sends high-frequency sound waves into the body via a transducer. The returning echoes are recorded and used to build an image of an internal structure. 3-D scanning uses a computer to return more detailed images.