UK multicentre project on assessment of risk of trisomy 21 by maternal age and fetal nuchal-translucency thickness at 10-14 weeks of gestation. Fetal Medicine Foundation First Trimester Screening Group

Lancet. 1998 Aug 1;352(9125):343-6. doi: 10.1016/s0140-6736(97)11280-6.


Background: Prenatal diagnosis of trisomy 21 currently relies on assessment of risk followed by invasive testing in the 5% of pregnancies at the highest estimated risk. Selection of the high-risk group by a combination of maternal age and second-trimester maternal serum biochemistry gives a detection rate of about 60%. We investigated assessment of risk by a combination of maternal age and fetal nuchal-translucency thickness, measured by ultrasonography at 10-14 weeks of gestation.

Methods: The risk of trisomy 21 was estimated for 96127 women of median age 31 years (range 14-49) with singleton pregnancies. Ultrasonography was done by 306 appropriately trained sonographers in 22 centres. Risk of trisomy 21 was calculated from the maternal age and gestational-age-related prevalence, multiplied by a likelihood ratio depending on the deviation from normal in nuchal-translucency thickness for crown-rump length. The distribution of risks was investigated and the sensitivity of a cut-off risk of 1 in 300 was calculated. Phenotype was assessed by fetal karyotyping or clinical examination of liveborn infants.

Findings: The estimated trisomy-21 risk, from maternal age and fetal nuchal-translucency thickness, was 1 in 300 or higher in 7907 (8.3%) of 95476 normal pregnancies, 268 (82-2%) of 326 with trisomy 21, and 253 (77.9%) of 325 with other chromosomal defects. The 5% of the study population with the highest estimated risk included 77% of trisomy-21 cases.

Interpretation: Selection of the high-risk group for invasive testing by this method allows the detection of about 80% of affected pregnancies. However, even this method of risk assessment requires about 30 invasive tests for identification of one affected fetus.

Publication types

  • Multicenter Study
  • Research Support, Non-U.S. Gov't
  • Comment

MeSH terms

  • Adolescent
  • Adult
  • Chromosome Aberrations
  • Chromosome Disorders
  • Crown-Rump Length
  • Down Syndrome / diagnosis*
  • Down Syndrome / diagnostic imaging
  • Female
  • Fetus / anatomy & histology*
  • Follow-Up Studies
  • Gestational Age*
  • Humans
  • Karyotyping
  • Likelihood Functions
  • Maternal Age*
  • Middle Aged
  • Neck / diagnostic imaging
  • Neck / embryology*
  • Phenotype
  • Predictive Value of Tests
  • Pregnancy
  • Pregnancy Outcome
  • Pregnant Women
  • Prevalence
  • Risk Assessment*
  • Sensitivity and Specificity
  • Ultrasonography, Prenatal*
  • United Kingdom