Ultrasound scan at 18 to 22 weeks of pregnancy

At 18 to 22 weeks of pregnancy the fetus weighs almost 1 pound and is about 10 inches long. Thanks to the size of the fetus the scan helps to make a thorough examination of baby's anatomy for normality and to reveal most anomalies demanding surgical correction or leading to low quality of postnatal life. In addition during this scan the markers of Down syndrome and other chromosomal abnormalities are searched. The appearance of many fetal organs is changed while having Down syndrome. The fetal anatomy survey helps to estimate whether the fetus has a high probability to have Down syndrome and to recommend detailed investigation (invasive tests) for Down syndrome if needed.

After the scan most concerns of the prenatal diagnosis are satisfied.

Besides during the 18-22 week scan the quantity of amniotic fluid is measured and the placenta is checked for its position and structure. With the help of the transvaginal probe the length of the cervix can be measured accurately. Knowing the length of the cervix a doctor can determine the risk of preterm birth. Especially this study is recommended to the women who have already had a preterm birth, surgery on the cervix, as well as to those who have multiple pregnancy.