The best time to observe the fetal heart is from 20 weeks to 24 weeks, because this is the period when better image quality is obtained relative to the observation of the structure, blood flow, and function of the fetal heart. Because the fetal heart is less than the size of an adult thumb at about 20 weeks, it is difficult to display and examine it under the influence of fetal movement, placenta, and maternal abdominal wall. Instead, the 32-week examination is mainly better for observation of valve stenosis-type lesions, especially for follow-up observation of suspected valve stenosis-type lesions at mid-pregnancy. This is because as the baby’s heart develops, the severity of the stenosis-type lesions will change, which is beneficial for the assessment of the baby’s prognosis as well as the judgment.