High-resolution ultrasonography may allow detection of the following: Renal malformations (eg, renal agenesis [Potter syndrome], polycystic kidney disease) Lethal forms of short-limbed skeletal dysplasias (eg, thanatophoric skeletal dysplasia, achondrogenesis) Gut malformations (eg, obstruction) Diaphragmatic hernia Microcephaly Hydrocephalus During the 2nd trimester, identifying structures that are statistically associated with increased risk of fetal chromosomal abnormalities helps refine risk estimate.