Rjm. Snijders et al., FETAL MILD HYDRONEPHROSIS AND CHROMOSOMAL DEFECTS - RELATION TO MATERNAL AGE AND GESTATION, Fetal diagnosis and therapy, 10(6), 1995, pp. 349-355
The presence of multiple ultrasonographic abnormalities is associated
with a significantly increased risk of chromosomal defects, while for
isolated abnormalities, the association is less clear. In a study of 1
,177 fetuses with mild hydronephrosis at 16-26 weeks of gestation, the
fetal karyotype was abnormal in 86 (7.3%) of the cases and the most c
ommon chromosomal defects were trisomies 21, 18 and 13. The frequency
of chromosomal defects increased with the number of additional abnorma
lities and for each chromosomal defect there was a characteristic patt
ern of associated abnormalities. However, in the 805 fetuses with appa
rently isolated hydronephrosis there were 5 (0.62%) with trisomy 21. O
n the basis of the maternal age and gestational age distribution of th
e population the expected frequency of trisomy 21 was 0.40%, which was
not significantly different from the observed (0.62%). To demonstrate
that such a difference is significant, it would be necessary to inves
tigate at least 1 million pregnancies. In the meantime, parents could
be counselled that the presence of mild hydronephrosis does not increa
se significantly the risk that the fetus has trisomy 21. Alternatively
, the risk is 1.6 times higher than the maternal age and gestational a
ge-related risk.