First-trimester screening for aneuploidy with fetal nuchal translucency in a United States population.

OBJECTIVE: To examine the detection rate of chromosomal abnormalities using a combination of nuchal translucency (NT) and maternal age in a United States population.

METHODS: A total of 2131 pregnancies with 2339 fetuses underwent NT screening from April 2000 to April 2002 in our ultrasound unit. Nuchal translucency was measured from 11 to 14 weeks' gestation. Fetal crown-rump length (CRL) was also measured. The risk for trisomy 21 was calculated from a combination of maternal age and fetal NT with the use of software provided by The Fetal Medicine Foundation (FMF). Sensitivity and false-positive rates were calculated for different risk cut-offs.

RESULTS: Chromosomal defects were diagnosed in 32 cases, including 12 cases of trisomy 21 and 10 cases of trisomy 18. The estimated risk based on maternal age and fetal NT was 1 in 300 or greater in 195 (8.3%) cases and these included 10/12 (83.3%) pregnancies with trisomy 21 and 9/10 (90.0%) pregnancies with trisomy 18.

CONCLUSION: A combination of maternal age and fetal NT provides an effective method of screening for chromosomal defects. Using ultrasound techniques and risk algorithms from The FMF, the performance of the test in an American population is similar to that described in international populations.