When a pregnant woman has an ultrasound to check the development of the fetus, she does not need to have an empty stomach. In early pregnancy not more than three months, the uterus does not change much, and at this time the ultrasound is done as usual, you need to drink water and hold urine to fill the bladder and observe the development of the gestational sac and fetal bud. If the fetal development is checked in the middle and late pregnancy, no preparation is needed and the examination can be performed at any time. However, it should be noted that if placenta previa or hypoplasia is suspected during the examination, it is also necessary for the pregnant woman to hold urine in appropriate amount to let the inner cervical opening show clearly and observe the position of the lower edge of the placenta to exclude placenta previa. If a pregnant woman wants to examine the digestive system, she needs to fast for at least 4-6 hours to observe the liver, gallbladder, pancreas and spleen. If a pregnant woman wants to examine the heart vessels and other superficial organs, she also does not need to fast and can do so at any time.