You do not need to hold your urine for an ultrasound at 12 weeks of pregnancy. At this gestational month, the uterus has enlarged beyond the pelvis and the fundus can usually be palpated just above the pubic symphysis. At 12 weeks of pregnancy, ultrasound can be used to rule out serious fetal anomalies, such as anencephaly. Ultrasound allows determination of the nuchal translucency (NT) and nasal bone length, and in combination with maternal age and laboratory tests, allows a comprehensive assessment of the risk of fetal chromosomal abnormalities. It is generally recommended for all pregnant women to have a systematic ultrasound examination of all fetal organs at 18-24 weeks of gestation, which usually includes examination of the skull, nose, eyes, heart, liver, kidneys, bladder, spine, extremities, etc., as well as examination of fetal appendages, such as placenta, umbilical cord, amniotic fluid, etc.