[Ultrasound screening for Down syndrome and other chromosomal abnormalities by fetal nuchal translucency measurement between 11-14 weeks of gestation].

AIM

To assess the feasibility of nuchal translucency [NT] measurement as a screening tool for Down syndrome [DS] and other chromosomal anomalies [ChA] between 11-14 weeks of gestation [w.g.].

MATERIALS AND METHODS

A longitudinal prospective follow up study was carried out at a tertiary referral center including 408 singleton pregnancies between 11+0 and 14+0 w.g. Three experienced sonographers performed transabdominal and/or transvaginal scans using high-resolution ultrasound equipment. The ultrasound examinations included assessment of fetal number and viability, NT measurement and fetal anatomy survey. Down syndrome [DS] risk was calculated using the specialized computer program provided by the Fetal Medicine Foundation [FMF], UK. In cases of estimated DS risk > or = 1:300 invasive prenatal diagnosis was offered--chorionic villus sampling [CVS] between 11-14 w.g. or amniocentesis [AC] after 15 w. g., as well as follow-up scans including fetal echocardiography. The samples were tested by cytogenetic analysis, DNA analysis and/or FISH. When chromosomal fetal abnormality was detected termination of pregnancy was an option. Pregnancy outcome was ascertained from hospital records, referring physicians or the patients themselves.

RESULTS

108 (26%) out of the 408 women were ?35 years and 300 (74%)--below that age. A total number of 9 fetal chromosomal anomalies [ChA] were found including 6 cases with DS, 2--with trisomy 18 [T18] and 1--with Turner syndrome. The overall sensitivity for DS was 66.7% for a false-positive rate [FPR] of 13.4%. The figures for all ChA were 77.7% and 12.8%, respectively. All three cases of ChA other than DS were in the screen-positive group. The overall sensitivity and FPR for ChA for patients > or = 35 years was 80% and 35%, while for patients < 35 years it was 75% and 5.1 %, respectively. Diagnostic invasive procedures were performed in 50 out of 58 screen-positive cases, including 7 of the cases with ChA. In all 7 cases with prenatal diagnosis of fetal ChA the parents chose to terminate the pregnancy.

CONCLUSIONS

First trimester DS screening by NT measurement has high sensitivity and specificity. Screening for other chromosomal abnormalities missed by second trimester biochemical serum tests is also possible. Invasive prenatal diagnosis is performed at an early gestational age when termination of affected pregnancies by D&C is still an option. Other important advantages are the possibility of screening for ChA in multiple gestations, as well as early diagnosis of major fetal anomalies.