During an ultrasound, high frequency sound waves are transmitted through the skin and bounce back as pictures on a monitor screen. Most women will have two ultrasounds during a pregnancy, one in the first trimester and another at around 20 weeks. At the 20 week ultrasound, the sex of the baby might be seen. The 20 week ultrasound is also a very important screening tool. Measurements of organs, limbs and cardiac evaluation are done. We want this to be a pleasant experience, but please understand this is a crucial evaluation of your baby. Please limit observers and be understanding if impatient siblings are asked to be removed from the ultrasound room.