Detection of genetic abnormalities by using CVS and FISH prior to fetal reduction in sonographically normal appearing fetuses.

OBJECTIVE

To examine the ability of chorionic villus sampling (CVS) and fluorescence in situ hybridization (FISH) to detect aneuploidy before first trimester fetal reduction (FR) in sonographically normal-appearing fetuses.

METHODS

A retrospective review of 470 patients referred to our unit for FR from January 2007-March 2011. Prenatal diagnosis was offered to all. FR was performed after next-day FISH results. Abnormalities were categorized by ultrasound, FISH, and/or karyotype. Sensitivity, specificity, positive predictive value, and negative predictive value of pre-FR FISH were calculated.

RESULTS

Four hundred thirty-two of 470 patients seen were first trimester. 24/432 (5.2%) were excluded for abnormal ultrasound findings, including nuchal translucency (NT) > 3.0 mm, and 360 (88.2%) underwent CVS before FR. Ten fetuses were then excluded for euploid sex mosaicism. 10/350 (2.9%) patients with normal ultrasounds had abnormal FISH confirmed by karyotype. 9/350 (2.6%) patients with normal FISH had an abnormal karyotype necessitating follow up amniocentesis in which the clinically relevant discordancy was confirmed in one case (1/350, 0.3%). Pre-FR FISH had a 90% sensitivity, 99.4% specificity, 83.3% positive predictive value, and 99.7% negative predictive value.

CONCLUSIONS

3.1% of patients with normal-appearing fetuses prior to first trimester FR had a fetus with an abnormal karyotype of which FISH detected 90%. CVS with FISH prior to FR adds significant information that can guide reduction decisions.