A prenatal ultrasound is a painless imaging test that employs sound wave technology to visualize the pelvic organs and fetus during pregnancy. Here, a special gel is applied to the exterior of the abdomen and a hand-held transducer device (or wand) is glided over the area to produce 2D and 3D images on a computer screen. To get the clearest results, women undergoing prenatal ultrasound may be instructed to fill their bladder by drinking several cups of water within an hour of the procedure. Prenatal ultrasounds performed during the first 12 weeks of a pregnancy can help determine how far along the pregnancy is, whether there is more than one fetus, or if there are any detectable problems including the possibility of Down syndrome. When performed later in the pregnancy, this test may be used to determine the baby’s sex, evaluate fetal growth and development, and visualize the interior of the pelvis including the placenta.