Edwards syndrome (Trisomy 18)

A 37-year-old woman, gravida 2, para 1, comes to the office for the evaluation of abnormal laboratory and sonogram results. She previously had a regular menstrual period every 28 days and is currently at 18 weeks gestation. She regularly takes prenatal vitamins and has no other medical conditions. Vital signs are within normal limits. A fetal anomaly scan performed one week ago was significant for polyhydramnios and intrauterine fetal growth restriction (IUGR). A second trimester quadruple screening test is performed at this visit, and the results are shown below:  
 

Laboratory value	Result
Maternal serum alpha fetoprotein	Low
Unconjugated estriol	Low
β-HCG	Low
Inhibin A	Low

Which of the following additional findings will likely be seen on the sonogram in this patient?