Definition: Fetal choroid plexus cysts are small, scattered, ≥3 mm diameter cysts found on ultrasound in the developing fetus in the lateral ventricular choroid plexus at 14-24 weeks of gestational age. Small cystic dilatations are seen in the lateral ventricular choroid plexus in 1-2% of fetuses. Typically, they are resolved by the end of midtrimester and lack clinical significance. However, a small percentage of choroid plexus cysts may be associated with 18-trisomy. Isolated choroid plexus cysts have a risk value of 1:374 for trisomy 18, with an increased risk of trisomy 18 if the age is older than 35 years. And the vast majority of fetuses with trisomy 18 are accompanied by other ultrasound detectable malformations. The detection of choroid plexus cysts should be judged in the context of the presence of other malformations, maternal age, and the results of midtrimester chromosomal screening. More than 90% of fetal choroid plexus cysts disappear after 26 weeks of gestation, with only a few increasing in size progressively. If they do not resolve after 26 weeks of gestation and are bilateral, fetal head MRI and chromosomal examination of umbilical cord blood cells should be performed to exclude chromosomal abnormalities such as trisomy 18 and trisomy 21.