Nearly a third of abnormalities found after first-trimester screening are different than expected: 10-year experience from a single center.

OBJECTIVE: This study aimed to assess the efficacy of first-trimester aneuploidy screening in a single clinical setting. METHODS: Maternal age, nuchal translucency, and maternal serum levels of pregnancy-associated plasma protein A and free beta human chorionic gonadotrophin comprised first-trimester risk assessment for Down syndrome and trisomies 13/18. Means, screen positive rates, detection rates, and predictive values were calculated for Down syndrome and trisomies 13/18. RESULTS: Of the 23 329 first-trimester screenings, 6.3% were screen positive: 5.7% for Down syndrome only, 0.4% for trisomies 13/18 only, and 0.3% for Down syndrome and trisomies 13/18. An abnormal karyotype was present in 3.9% of screen positives for Down syndrome, 13.8% of screen positives for trisomies 13/18, and 45.9% of screen positives for both Down syndrome and trisomies 13/18. Of the 97 pregnancies found to have an abnormal karyotype, 29.9% had chromosome abnormalities other than trisomy 13, 18, or 21, with expected clinical outcomes ranging from likely benign to uniformly lethal. CONCLUSION: As expected, first-trimester screening is effective for detecting aneuploidy for chromosomes 13, 18, and 21; however, a significant number of chromosomally abnormal pregnancies initially identified by first-trimester screening have a different karyotype. With the possible exception of 47,XYY and 45,X, the dataset suggested that these different chromosome complements were likely to be randomly distributed. Nevertheless, prior to diagnostic testing, prospective parents should be counseled concerning the possibility of a chromosome abnormality other than the trisomies 13, 18, or 21.

Increased nuchal translucency in the presence of normal chromosomes: what's next?

PURPOSE OF REVIEW: First trimester screening is presently offered to all pregnant women as a means of prenatal screening for Down syndrome, trisomy 18, and trisomy 13. Nuchal translucency measurement is a fundamental component of the screening protocol. A woman whose fetus' nuchal translucency is greater than the 95th percentile is also at increased risk for a multiplicity of other adverse pregnancy and pediatric outcomes, and as a consequence, counseling of patients about their testing options and range of pregnancy outcomes has become complex and difficult. RECENT FINDINGS: The increased risk for chromosome abnormalities, congenital heart malformations, and pregnancy loss in the presence of an increased nuchal translucency is well documented. What has not been clearly defined is the incidence of other genetic syndromes, congenital defects, and adverse pregnancy and pediatric outcomes in the presence of increased nuchal translucency. Currently, Noonan syndrome is the only molecular genetic condition that has been shown to have a clear association with the finding of increased nuchal translucency in the first trimester. SUMMARY: This article reviews the current literature on outcomes in pregnancies with an increased nuchal translucency and a normal karyotype. We summarize the range of outcomes detected in the first trimester with recommendations for further prenatal testing and counseling of patients.