ABSTRACT
The purpose was to study nuchal translucency thickness of normal Thai fetuses in the first trimester. From January 1996 to June 1999, there were 1,970 pregnant women, whose gestational ages were between 10 to 13(+6) weeks of gestation, who attended the Down syndrome screening clinic. Nuchal translucency (NT) thickness measurement was used as the screening method for Down syndrome. When the result showed an increased risk for Down syndrome, the patient was counselled and the invasive test for the definite diagnosis was optional. Pregnant women who had had an abortion and/or congenital anomaly babies were excluded. Only pregnant women who had normal newborns were recruited in this study. There were 1,631 pregnant women who had normal newborns in this study. The mean maternal age was 28.70 +/- 5.14 years. There were 222 (13.6%) pregnant women whose ages were more than or equal to 35 years. There was quadratic correlation of an increase in nuchal translucency and the crown-rump length (CRL) in normal fetuses in the first trimester. The quadratic equation was log10 NT = 1,215 x 10(-4) CRL-8.7 x 10(-4) CRL(2)-3.7037. The normal fetuses with nuchal translucency thickness more than or equal to 2.5 mm were found in 1.23 per cent in this study. In conclusion, there was quadratic correlation of nuchal translucency thickness and crown-rump length of first trimester fetuses in a Thai population.