The Principles of Clinical Cytogenetics - Extra Materials - Springer

Prenatal Cytogenetics 297
A study in Denmark (174) showed the combination of nuchal translucency and visualization of the
nasal bone between 11 and 14 weeks to be as good a predictive marker as nuchal translucency and
biochemical markers. Zoppi et al. evaluated other fetal chromosome abnormalities with regard to
nonvisible nasal bone and found the bone not to be visible in four out of five trisomy 18 fetuses, two
out of three Turner syndrome fetuses, and in 0.2% of fetuses with normal karyotypes (170).
The literature to date suggests that when adequate visualization is possible, which occurs in 91.9–
98.9% of series, absent or hypoplastic nasal bone is seen in 60–80% of fetuses with trisomy 21.
Bunduki et al. (175) performed ultrasound examinations on 1923 consecutive singleton pregnancies
at 16–24 weeks and noted that nasal bone length increased as a function of gestational age, showing
a linear relationship. Screening for trisomy 21 using the 5th percentile as a cut-off value resulted in a
sensitivity of 59.1% for a 5.1% screen-positive rate. The likelihood ratio was 11.6.
A national collaborative study under the direction of Cicero is underway to evaluate this potentially
important ultrasound finding more thoroughly.
Renal Pyelectasis
Renal pyelectasis is mild dilation of the renal pelvis. A possible link between fetal renal pyelectasis
and trisomy 21 was described in 1990 (176). This led to other studies with conflicting results. In 1996,
Wickstrom et al. (177) published a prospective study of 7481 patients referred for prenatal ultrasound
evaluation. Of these, 121 (1.6%) had isolated fetal pyelectasis (defined as � 4 mm before 33 weeks’
gestation and � 7 mm at 33 weeks’ gestation). This compares with prevalences of 1.1–18% in other
studies. Of the 121, 99 karyotypes were available. One of these was trisomy 21 and another was mosaic
47,XYY/46,XY. Based on maternal age and the baseline risk for trisomy 21 in the population, the
authors calculated a relative risk of 3.9 for trisomy 21 when isolated renal pyelectasis is seen and a 3.3fold
increase in risk for all chromosomal abnormalities in the presence of isolated fetal pyelectasis.
Corteville et al. (178) studied 5944 fetuses for the presence of pyelectasis, defined as an anteroposterior
renal pelvic diameter of 4 mm or greater before 33 weeks or 7 mm or greater after 33 weeks, the same
definition as was used by Wickstrom et al. (177). Pyelectasis was seen in 4 of 23 (17.4%) of trisomy 21
fetuses and in 120 of 5876 (2%) of normal controls. This was statistically significant at p