[Combined use of nuchal translucency, gestational age and maternal age for evaluation of the risk of trisomy 21].
OBJECTIVE
Despite the definition of new screening policies for fetal trisomies, based on nuchal translucency thickness (NT) or maternal serum, the prevalence of trisomy 21 remains high. We propose a strategy based on a combination of maternal age, gestational age and NT, measured at the first trimester ultrasound examination, for the assessment of risk.


METHODS
We present, in this paper, a characterisation of the physiological increase of fetal NT between the 10th and the 14th week of gestation, in a preliminary study of 266 echographic examinations. Next we propose a calculation of the simultaneous risk of trisomy 21 based on marginal risks for maternal age and increased NT values available in the literature.


CONCLUSIONS
We propose to define a high-risk group associated to the NT marker by using a cut-off risk of 1/250 for the simultaneous risk. This criteria may, as well, be expressed by a pathological threshold of NT varying with maternal age and gestational age. Without questioning that women aged of 38 years or older are a high-risk group, this approach should allow an improvement of the prenatal screening for trisomy 21.
Faraut
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Techniques de l'Imagerie de la Modélisation et de la Cognition (TIMC), Faculté de Médecine, La Tronche.
Cans
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Althuser
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Jouk
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D000328:Adult; D004314:Down Syndrome / Q000453:epidemiology*; D005069:Evaluation Studies as Topic; D005260:Female; D005602:France / Q000453:epidemiology; D005865:Gestational Age; D006801:Humans; D008403:Mass Screening / Q000379:methods*; D008423:Maternal Age; D008875:Middle Aged; D009333:Neck / Q000000981:diagnostic imaging / Q000196:embryology*; D011247:Pregnancy; D018566:Pregnancy, High-Risk; D015995:Prevalence; D012307:Risk Factors; D016216:Ultrasonography, Prenatal