Neural tube defects and omphalocele in trisomy 18.

A trisomy 18 fetus with severe congenital anomalies including craniorachischisis, large omphalocele, and bilateral cleft lip and palate is reported. The occurrence of neural tube defects and/or omphalocele in reported cases of trisomy 18 is discussed and the frequency of these anomalies in 85 trisomy 18 patients evaluated at Indiana University School of Medicine from 1963 to 1986 is reviewed. In this series of patients the frequency of neural tube defects was 7.0% and the frequency of omphaloceles was 5.9%. The percentage of these findings in our cases supports the premise that neural tube defects and omphaloceles are part of the trisomy 18 phenotype. Since fetuses with trisomy 18 are subject to early fetal loss or premature birth, the more subtle physical features of this condition may not be apparent. Thus, karyotyping of fetuses and premature infants with either neural tube defect or omphalocele should be considered.