Correlation between nuchal thickness and abnormal karyotype in first trimester fetuses.
OBJECTIVE
To evaluate the accuracy of ultrasound measurement of nuchal thickness in first trimester fetuses for predicting fetal karyotype.


METHODS
A prospective study of the nuchal thickness of fetuses measured during an ultrasound examination in all women undergoing first trimester chorionic villus sampling (CVS).


METHODS
Two major public hospitals and two associated private practices between 7 September 1993 and 6 September 1994.


METHODS
Pregnant women with various indications for CVS (in 82% because of maternal age).


RESULTS
1306 women underwent CVS, including 11 with twin pregnancies: 1317 fetuses were tested. Karyotype results were obtained for 1312 fetuses: 41 (3.1%) had an abnormal karyotype, and 20 of these (49%) had a nuchal thickness measurement of 3 mm or more, compared with 44 (3.5%) of the 1271 fetuses with a normal karyotype. Of the 21 fetuses shown to have trisomy 21, 12 would have been detected if a nuchal thickness of 3 mm or more had been used as an indicator, giving a sensitivity of 57%. Nuchal thickness measurements of 1 or 2 mm excluded trisomy 21 with a negative predictive value of 99.3%. Fetuses with moderate nuchal thickening, normal karyotype and no other problems noted on the initial ultrasound scan had neonatal outcomes similar to those in the general obstetric population.


CONCLUSIONS
Nuchal thickening in the first trimester (10 weeks on) of pregnancy in a high risk population is a powerful indicator of increased risk of aneuploidy.
Ultrasound Department, Royal Women's Hospital, Melbourne, VIC.
B G
BG
Hewitt
L
L
de Crespigny
A J
AJ
Sampson
A C
AC
Ngu
P
P
Shekleton
H P
HP
Robinson
D000328:Adult; D000782:Aneuploidy; D015193:Chorionic Villi Sampling; D005260:Female; D005333:Fetus / Q000196:embryology* / Q000648:ultrastructure; D005865:Gestational Age; D006801:Humans; D007621:Karyotyping; D008423:Maternal Age; D008875:Middle Aged; D009333:Neck / Q000000981:diagnostic imaging* / Q000196:embryology; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011379:Prognosis; D011446:Prospective Studies; D016216:Ultrasonography, Prenatal