Ultrasound for Fetal Aneuploidy in the First and Second Trimesters

Ultrasound cannot be used to confirm or exclude a diagnosis of chromosomal anomalies like aneuploidy. But ultrasound can be used to further modify the risk that already exists by age or serum screening. Measurement of nucal translucency alone in the first trimester is less effective for first trimester screening. For monochorionic twins there's no evidence based recommendations on the frequency of fetal growth scans after 20 weeks but it seems reasonable according to the college to perform serial ultrasound surveillance every 4 to 6 weeks, if possible.