First-trimester growth patterns of aneuploid fetuses.

First-trimester growth restriction has been reported in certain aneuploid pregnancies. The purpose of this study was to evaluate this association further by comparing the crown-rump lengths (CRLs) and growth rates from 196 chromosomally abnormal fetuses with a control population of 1929 euploid fetuses. The mean CRLs and growth rates were significantly reduced (P < 0.05) in the groups of fetuses with trisomy 18 (n = 49), trisomy 13 (n = 19), and triploidy (n = 8). Using a fifth percentile cut-off, growth rate was a better discriminator than a single CRL in identifying fetuses affected with these aneuploidies. These growth parameters were not significantly reduced in fetuses with trisomy 21 (n = 92), sex chromosome trisomies (n = 20), or 45,X (n = 8). We conclude that fetal growth restriction associated with an underlying chromosome abnormality can occur as early as the first trimester. This phenomenon results from intrinsic fetal factors and not delayed ovulation. Such information is important to establish as first-trimester serum screening evolves.