Evaluating the incidence and likelihood ratios for chromosomal abnormalities in fetuses with common central nervous system malformations

OBJECTIVE: To determine the incidence and likelihood ratios for chromosomal abnormalities in fetuses with common central nervous system malformations on ultrasound. STUDY DESIGN: A database derived retrospective cohort study of all patients referred for ultrasound and genetic evaluation from 1990-2006. Fetal karyotypes were delineated by prenatal diagnosis or postnatal examination. The incidence and likelihood ratios were calculated for the association of each central nervous system abnormality with trisomy 13, 18, and 21. RESULTS: Of 62,111 women included, 587 (0.9%) had major fetal central nervous system abnormalities. The only central nervous system anomalies associated with trisomy 21 were ventriculomegaly and choroid plexus cysts. When isolated, only spina bifida, holoprosencephaly, and agenesis of the corpus callosum were significantly associated with trisomy 13, anencephaly with trisomy 18, and ventriculomegaly with trisomy 21. Likelihood ratios positive range from 2-20 depending on the central nervous system malformation and aneuploidy type. CONCLUSION: Central nervous system malformations detected on ultrasound are strongly associated with and predictive of chromosomal abnormalities, especially trisomy 13 and 18.