For every expectant father and mother, welcoming the arrival of a new life is a long-awaited thing, which also means there are more new skills to learn. To ensure that children come to this world safely and healthily, prenatal examination is a compulsory course for expectant parents. Today, from the perspective of ultrasound medicine, we will talk about what prenatal examinations need to be done and why the birth of congenital defects cannot be completely avoided. Is ultrasound safe for fetuses? The frequency range of sound that can be heard by the human ear is 20-20000Hz, while ultrasound refers to a mechanical wave with a frequency greater than 20000Hz and exceeding the upper limit of the auditory threshold of the human ear. Usually, the ultrasonic energy used during physical examinations is very small and the duration of action is very short. Therefore, ultrasound examination is currently recognized worldwide as the safest, simplest, and most practical examination method for fetuses, and there have been no reports of fetal malformation or death caused by ultrasound examination. Although ultrasound examination is safe and harmless for the fetus, it is not advisable to frequently use ultrasound examination to explore the fetal status due to excessive tension and anxiety, as fetal growth and development are dynamic processes that can be mastered at key developmental nodes. Under normal circumstances, at least 5 to 6 prenatal ultrasound examinations are required throughout the entire pregnancy. The main purpose of ultrasound examination at 6-8 weeks of pregnancy is to clarify the implantation position of the fetal sac, check for fetal buds and fetal heart rate (i.e. whether the fetus is alive), and rule out abnormal pregnancy, such as ectopic pregnancy, hydatidiform mole, fetal arrest, etc; Determine the number of embryos and check the gestational age; Check if pregnant women have uterine fibroids, ovarian cysts, etc. 2. Pregnancy from 11 weeks to 13 weeks+6 days is mainly used to measure the thickness of the nuchal translucency (NT) of the fetus. The safe value range is NT ≤ 2.5mm, and NT>2.5mm indicates abnormal thickening, indicating a possible risk of chromosomal abnormalities. Chromosome screening should be increased to exclude congenital Down syndrome. At the same time, ultrasound examination at this time can also detect early major abnormalities, such as anencephaly, complex congenital heart disease, and obvious limb absence. 3. Systematic ultrasound screening of fetuses at 20-24 weeks of pregnancy is an important examination throughout the entire pregnancy period. Ultrasound doctors not only perform routine examinations on the size of the fetus and its appendages (umbilical cord, placenta, amniotic fluid, etc.), but also examine specific structures of the fetus, including intracranial structures (lateral ventricles, cerebellum, posterior fossa cistern, etc.), as well as skull, orbit, nasal bone, upper lip, lungs, heart, gastric vesicle, kidneys, bladder, limbs, spine, abdominal wall, etc., in order to rule out major abnormalities in various systems of the fetus, hence it is often referred to as "major malformations". 4. Screening for fetal growth and development between 28 and 32 weeks of pregnancy, further evaluating fetal organs, commonly known as "minor ovulation", is a missed diagnosis of "major ovulation". 5. At least one ultrasound should be performed near or after full term pregnancy, with some pregnant women requiring 2-3 ultrasound tests. The main purpose is to evaluate the growth and development of the fetus, placental maturity, suitability of amniotic fluid volume, normal fetal position, and estimation of fetal weight, providing reference for obstetrics in selecting delivery methods