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Excerpt
We performed this data review to determine the prevalence of karyotype abnormalities in a group of fetuses with prenatally detected open spina bifida and to assess the ability of prenatal sonography to enable prediction of which fetuses may have chromosomal abnormalities.
From 1985 to 1991, 63 fetuses with open spina bifida were examined in our sonographic laboratory. The sonographic images were retrospectively reviewed. Gestational ages of our fetuses ranged from 17.6 to 40.0 weeks. All sonographic abnormalities, in addition to the spina bifida and its associated cranial and lower extremity findings, were recorded.
Of the 63 fetuses with open spina bifida, chromosome information was available for 52. Forty-three of 52 fetuses (83 percent) had normal chromosomes, and nine (17 percent) had abnormal chromosomes.
In the nine fetuses with abnormal chromosomes, karyotype abnormalities included five with trisomy 18, two with trisomy 13, and one each with triploidy and translocation. Eight of those nine fetuses had other sonographic abnormalities in addition to spina bifida and its associated cranial and lower extermity findings: four with intrauterine growth retardation, three with omphalocele, two with a two-vessel cord, and one each with ventricular septal defect, echogenic kidneys, hydronephrosis, nonvisible fetal urinary bladder, and hydropic placenta.
Of the 43 fetuses with normal chromosomes, 38 had sonographically isolated spina bifida. Twenty of these fetuses underwent destructive pregnancy termination that precluded pathologic confirmation, three were lost to follow-up, and one was found at autopsy to have a Dandy-Walker malformation that had escaped sonographic detection. Of the remaining five fetuses with normal chromosomes, four had associated sonographic abnormalities that were identified prenatally, and one fetus was incompletely scanned because it was a twin referred for selective termination only. The associated sonographic abnormalities identified in the first four fetuses were dilated bladder with hydronephrosis versus cystic dysplasia, omphalocele, holoprosencephaly, and choroid plexus cyst.
Of the 11 fetuses for whom karyotype information was not available, six had sonographically isolated spina bifida and destructive pregnancy terminations precluded pathologic follow-up and four were lost to follow-up. In the final fetus, additional sonographic findings included a congenital cystic adenomatoid malformation and a posterior patella.
Overall, additional abnormalities were identified at sonography in 15 of 63 fetuses (24 percent) when third-trimester intrauterine growth retardation is included. If we consider only the 52 fetuses for whom we have karyotype information, additional abnormalities were identified in 12. Eight of these 12 fetuses had abnormal chromosomes. Excluding third-trimester intrauterine growth retardation as an associated abnormality, 11 fetuses with known chromosomes had additional sonographically detected abnormalities. Seven of these had abnormal chromosomes. Thus, two of nine fetuses with abnormal chromosomes had sonographically isolated spina bifida. Therefore, in our group of fetuses with prenatally detected spina bifida, the positive predictive value for additional sonographic abnormalities to be predictive of a karyotype abnormality was 64 percent, and the negative predictive value when additional sonographic findings were absent was 95 percent.
