Prenatal ultrasound detection of isolated neural tube defects: is cytogenetic evaluation warranted?

To determine the value of cytogenetic evaluation in fetuses with isolated neural tube defects diagnosed by prenatal ultrasound.

Fifty-five thousand two hundred sixty obstetric ultrasounds performed for various indications at the Indiana University Prenatal Diagnostic Center from July 1988 to March 1994 were reviewed using a computerized data base. Excluding all cases of anencephaly, fetuses with isolated neural tube defects were identified. Maternal demographic data, pregnancy outcomes, level of defect, and fetal karyotype when available were obtained. Statistical analysis was performed using the chi 2 test, when appropriate. P < or = .05 was considered statistically significant.

Seventy-seven medical record charts of women with prenatally diagnosed isolated fetal neural tube defects were reviewed. Nineteen pregnancies were terminated, 42 pregnancies were delivered, and 16 pregnancies were lost to follow-up. Karyotypes were available in 43 of the 77 cases (55.8%). The theoretical risk of chromosomal anomalies in this sample population based solely on maternal age was 0.3%. Of the 43 documented karyotypes, seven chromosomal anomalies were discovered (16.3%). The difference was statistically significant (P = .012). Detected chromosomal anomalies included two trisomy 18, two triploid 69,XXX, one triploid 69,XXY, one balanced Robertsonian translocation t(13q,14q), and one inversion in the q arm of the X chromosome.

The prevalence of karyotypic abnormalities is significantly increased in fetuses with isolated neural tube defects; therefore, prompt antenatal genetic evaluation should be considered in such cases.