Early midtrimester fetal nuchal thickness: effectiveness as a marker of Down syndrome.
OBJECTIVE
Our purpose was to assess the validity of nuchal thickness in the prediction of Down syndrome in early midtrimester fetuses.


METHODS
In 1543 consecutive pregnancies undergoing amniocentesis, primarily for advanced maternal age, nuchal thickness was prospectively measured between 13 and 18 weeks and then correlated with the karyotype obtained from amniotic fluid.


RESULTS
With the cutoff value suggested in the literature (> or = 6 mm), 33.3% (6/18) of the cases of Down syndrome would be detected for a 0.1% (2/1424) false-positive rate, with a positive predictive value adjusted to a prevalence of Down syndrome in the general population of 1:3. To increase the sensitivity of the method, the threshold was lowered to 5 mm, achieving a sensitivity of 77.8% (14/18) for a 2.1% (30/1424) false-positive rate and an adjusted positive value of 1:19.


CONCLUSIONS
In early midtrimester fetuses decreasing the nuchal thickness threshold to 5 mm substantially enhances the detection of Down syndrome with a reasonable false-positive rate.
Borrell
A
A
Department of Obstetrics and Gynecology, Hospital Clinic, University of Barcelona Medical School, Spain.
Costa
D
D
Martinez
J M
JM
Delgado
R D
RD
Casals
E
E
Ojuel
J
J
Fortuny
A
A
D004314:Down Syndrome / Q000000981:diagnostic imaging / Q000235:genetics / Q000473:pathology*; D005260:Female; D005865:Gestational Age; D006801:Humans; D009333:Neck / Q000473:pathology*; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011262:Pregnancy Trimester, Second; D011446:Prospective Studies; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal