In general, pregnant women only need to hold their urine during transabdominal ultrasound examinations in early pregnancy, but not usually at other times. However, there are some special cases where it is necessary to ask the doctor about the examination in advance to facilitate good preparation. In early pregnancy, it is necessary to hold urine because the uterus is relatively small and a full bladder is needed as a reference to determine the position of the uterus. However, if a vaginal ultrasound is done, there is no need to hold urine. As the gestational week increases, usually after 12 weeks of pregnancy, there is usually no need to hold urine for ultrasound at this time because the uterus has grown and amniotic fluid is present. However, if the placenta is low and the bladder is needed as a reference, the pregnant woman should hold her urine slightly for the test. In addition, there are some special cases when it is still necessary to hold urine for ultrasound. For example, if a pregnant woman has lower back pain and needs to rule out urinary tract diseases, holding urine can help to fill the bladder and facilitate the examination; if she has lower abdominal pain or vaginal bleeding in the middle or late pregnancy and needs to know the length of the uterus, holding urine can also facilitate the relevant tests. It is important to note that it is not recommended that pregnant women hold their urine frequently during pregnancy if not necessary. Occasional holding of urine by pregnant women has little effect, but long-term holding of urine may cause the bladder to lose its elasticity and urinary incontinence may occur, or overfilling of the bladder may compress the uterus and affect the fetus.