First-trimester growth restriction and fetal aneuploidy: the effect of type of aneuploidy and gestational age

Fetuses with fatal chromosomal defects may have a much shorter crown-rump length than normal fetuses or fetuses with Down syndrome. Researchers performed ultrasound analysis of the crown-rump length of 144 fetuses of nine to 13 weeks' gestation. These fetuses also underwent chorionic villus sampling because their mothers had histories of chromosomal abnormalities. Fetuses with trisomy 18 had a significantly shorter crown-rump length than did normal fetuses while fetuses with trisomy 13 had a somewhat shorter crown-rump length. Fetuses with Down syndrome, or trisomy 21, had a similar crown-rump length to that of normal fetuses.