[Value of nuchal translucency thickening in the fetal chromosome abnormality screening]

To investigate the value of nuchal translucency(NT) thickening in the fetal chromosome abnormality screening.

The 14 881 pregnant women received NT measurement in 11-13(+)6 weeks at Beijing Obstetrics and Gynecology Hospital from January 2010 to August 2012. The 118 fetuses whose NT ≥ 2.5 mm were recruited.One hundred and eight (91.5%, 108/118) of them accepted invasive procedure and karyotype analysis.

(1) Chromosome karyotype analysis: 113 singleton pregnancies (95.8%) and 5 twin pregnancies (4.2%) whose NT thickened from 2.5 mm to 11.0 mm were advised karyotype analysis. The 108 pregnant women accepted karyotype analysis. Among them, 88 had normal chromosome karyotype, and 20 had chromosome abnormalities. The detection rate was 18.5% (20/108).(2) The sensitivity, specificity, false positive rate, false negative rate, total consistent rate, positive predictive value and negative predictive value of prenatal screening of chromosome abnormalities for NT ≥ 2.5 mm were 44%, 99%, 1%, 56%, 99%, 19% and 100%, respectively.(3) Among the 88 fetuses who had normal karyotype, 72 (82%) had isolated thickened NT, while 16 (18%) had fetal structural malformation or intrauterine demise.(4) Among the 10 pregnant women who did not accept fetal karyotype analysis, 8 terminated pregnancy because of fetal structural malformation, and the other 2 fetuses died in uterus.(5) All of the 5 twin pregnancies were dichorionic twins, and one of the twins had thickened NT. Among the 5 twin pregnancies, one fetus was trisomy 21 and others had normal karyotype.3 twin pregnancies who had normal chromosomes gave live birth. And the other had a gastroschisis and exstrophy deformity fetuse. This fetuse died in uterus and remaining fetuse had full-term live birth.(6) 35 (29.7%) pregnant women received second trimester Down's syndrome serum screening.One was high risk and was proved a trisomy 21 pregnancy. Thirty-four were low risk and had normal chromosome karyotype.

NT thickening may indicate fetal chromosome abnormalities or other structural malformations. It is a useful prenatal screening indicator.