First-trimester tests for trisomies 21 and 18 as sensitive as triple screen
The Journal of Family Practice. 2004 March;53(3):172-188
March 1, 2004|The Journal of Family Practice
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- BACKGROUND: Women who are deemed to have abnormal calculated risks for trisomy 21 (Down syndrome—the most common trisomy) or trisomy 18 (Edwards syndrome, a much less common but more severe type of aneuploid pregnancy) and elect to undergo second-trimester triple screening are counseled on ultrasound and confirmatory fetal karyotype testing, typically amniocentesis.
- POPULATION STUDIED: Women at 12 academic prenatal diagnostic centers in the US and Canada who were between 10 4/7 and 13 6/7 weeks gestation were offered first-trimester screening if they met inclusion criteria: a singleton gestation that was not the product of a donor oocyte, no significant recent vaginal bleeding, no other indications for prenatal diagnosis, and no diabetes. A total of 8816 eligible patients consented.
- STUDY DESIGN AND VALIDITY: First-trimester screening consisted of maternal serum measurements of free beta human chorionic gonadotropin and pregnancy-associated plasma protein A, along with ultrasonographic measurement of fetal nuchal translucency. These biochemical markers and ultrasound measurement were analyzed independently and together to compute patient-specific risks.
- OUTCOMES MEASURED: The primary study outcomes were sensitivity and specificity of the first-trimester screening tools as determined by knowledge of fetal karyotype or newborn phenotype.
- RESULTS: The investigators found that a combination of maternal age, the 2 serum markers, and nuchal translucency in the first trimester was 89% sensitive and 89% specific for identification of trisomy 18 (11 cases) or 21 (61 cases). The stated sensitivity and specificity of second-trimester triple screen for trisomy 21 are 65% and 95%, respectively.
PRACTICE RECOMMENDATIONS
First-trimester screening for trisomies 21 and 18 with maternal serum markers and ultra-sonographic measurement of fetal nuchal translucency is more sensitive than second-trimester “triple screen.” Application of this finding to general practice is limited by lack of access to radiologists trained in this more specialized prenatal ultrasound measurement.
