First-trimester screening for chromosomal abnormalities by fetal nuchal translucency in a Brazilian population


  • Presented at The Fetal Medicine Foundation's meeting on Research and Developments in Fetal Medicine, London, August 30th–September 1st 2001.



To examine the detection rate of chromosomal abnormalities using nuchal translucency (NT) thickness in a Brazilian population.


This was a prospective study of 2996 singleton pregnancies with a live fetus at 10–14 weeks of gestation attending for routine antenatal care in a teaching hospital in Brazil. Fetal crown–rump length (CRL) and NT thickness were measured and the risks for trisomy 21 were calculated by a combination of maternal age and fetal NT with the use of software provided by The Fetal Medicine Foundation. Sensitivity and positive predictive values for different risk cut-offs were calculated.


Chromosomal defects were diagnosed in 22 cases, including 10 cases of trisomy 21. The estimated risk based on maternal age and fetal NT was 1 in 300 or greater in 222 (7.4%) cases and these included nine of 10 (90.0%) pregnancies with trisomy 21 and nine of 12 (75.0%) pregnancies with other chromosomal defects. The NT was above the 95th centile in 5.8% of cases and this group included 70% of the trisomy 21 cases.


A combination of maternal age and fetal NT provides an effective method of screening for chromosomal defects. The performance of the test in a Brazilian population is similar to that in Britain.Copyright © 2001 International Society of Ultrasound in Obstetrics and Gynecology