When to check ultrasound after pregnancy and how many times is appropriate: Regular ultrasound examination is necessary after pregnancy, and it is generally considered that ultrasound examination should be performed about 3 times during pregnancy without special circumstances. The first ultrasound examination can be performed in early pregnancy (around 45 days of gestation), which can accurately estimate whether the pregnancy is intrauterine or ectopic, determine whether the pregnancy is single or multiple, and whether the embryo development is in accordance with the gestational week. The second ultrasound examination is performed at 20 to 24 weeks of gestation and is mainly used to screen for fetal malformations. Because the fetal organs are fully developed at this time, a careful ultrasound examination can reveal any abnormalities of important organs and detect fetal malformations at an early stage. The third ultrasound can be used before delivery to assess the growth and development of the fetus and to understand the position of the placenta and the amount of amniotic fluid. However, if any abnormalities are found during pregnancy, such as suspected fetal abnormality, fetal development too large or too small, too much or too little amniotic fluid, abnormal placenta, or overdue pregnancy, ultrasound examination is needed at any time. The best time for prenatal ultrasound diagnosis of fetal malformation is during the middle of pregnancy, especially from 20 to 28 weeks. However, most pregnant women are not able to have routine ultrasound examination due to various reasons, and the first ultrasound is too late, which makes some malformed fetuses found only in larger months, causing great impact to the physical and mental health of pregnant women. Some pregnant women have normal ultrasound examination in early pregnancy, so they do not perform ultrasound monitoring regularly, and as a result, they cannot diagnose fetal malformations in time. Some pregnant women and even doctors think that more ultrasound will affect the development of the fetus, which is actually a misunderstanding of ultrasound. In fact, this is a misunderstanding of ultrasound. Generally, the time spent for ultrasound examination in early pregnancy is very short, and ultrasound after the middle and late pregnancy has basically no effect.