Many pregnant women feel very confused about the need to undergo both big anomaly screening and small anomaly screening during pregnancy, feeling that since both big anomaly screening and small anomaly screening contain the word "anomaly screening", they should both be for the purpose of screening malformed fetuses. However, why do they need to be done twice? In fact, big anomaly screening and small anomaly screening are different, and each examination is indispensable.

Fetal anomaly screening, simply put, is the examination to rule out the possibility of malformed infants that women undergo at hospitals or maternal and child health stations in the early stages of pregnancy. Generally speaking, pregnant women should undergo examination at around 20 weeks of pregnancy, and it is best not to exceed 28 weeks. Fetal anomaly screening is divided into small anomaly screening and big anomaly screening. The small anomaly screening is at 18 weeks of pregnancy, black and white B-ultrasound. While the fetal anomaly screening B-ultrasound is generally at 24 weeks of pregnancy, three-dimensional or four-dimensional color Doppler ultrasound, to examine the growth and development of various fetal organs, and at this time, the growth of various fetal organs is sound, the amniotic fluid is moderate, and the fetus is not too large, making it clear to see with three-dimensional (four-dimensional) ultrasound.

"Big anomaly screening" is a通俗 term, the standard term is "Mid-pregnancy systematic prenatal color Doppler examination". During the mid-pregnancy color Doppler examination, in addition to observing the growth and development of the fetus, the embryo, and the general condition of the amniotic fluid of the pregnant woman, a detailed examination of each fetal organ and system is also carried out, with the aim of determining whether the fetus has major structural defects, hence the name "big anomaly screening". The "big anomaly screening" should be done between 20-24 weeks of pregnancy. Firstly, at this time, most fetal structural abnormalities can be detected; secondly, if done too early, the fetus is relatively small, and the organs have not developed well enough to detect structural abnormalities.

Each ultrasound examination is a whole process of fetal anomaly screening, generally performed 3-4 times throughout the entire pregnancy, and if there are special circumstances, the frequency needs to be increased. The first: 6-8 weeks pregnant, to see if there is a fetal heartbeat and bud, to rule out ectopic pregnancy or abnormal pregnancy (such as hydatid mole), if there is no pregnancy with bleeding or abdominal pain, the first ultrasound can be skipped. The second: 11-14 weeks pregnant, to screen the fetal nuchal translucency, and to assess the risk of fetal chromosomal abnormalities. The third: 24-28 weeks pregnant, to perform a comprehensive fetal anomaly screening, including anencephaly, encephalocele, open spina bifida, chest wall defect with visceral organs protruding outside, single ventricle, and other malformations. This color Doppler examination is crucial. The fourth: 37-40 weeks pregnant, to grasp the size, position, placental location, maturity, amniotic fluid flow, and whether the fetus has the condition of umbilical cord around the neck.