Interpretation
The direct relationship of chromosomal anomalies with increasing nuchal
translucency measurements is well established in fetuses between 45 mm
and 84 mm in several studies.8, 9 However, there is
little known about this relationship in fetuses under 45 mm. A
prospective cohort study of 672 fetuses concluded that a nuchal
translucency measurement above the 95th percentile in
fetuses at 9 to 10 weeks could be used clinically as a marker for
aneuploidy.5 The authors reported that NT was above
95th percentile in 64% of the fetuses with trisomy
21, 71% of those with trisomy 13 or trisomy 18 and in all cases of
monosomy X.5 Scholl and Chasen10have compared the outcomes of fetuses with cystic hygroma both with CRL
< 45 mm and CRL ≥ 45 mm and concluded that the rate of
chromosomal abnormalities and birth outcomes were lower in the CRL
< 45 mm fetuses with cystic hygroma as compared to the ones
with CRL ≥ 45 mm. The cases in the mentioned study represent the extreme
end of the nuchal oedema group (median nuchal measurement 5.5
mm),10 while our cases included nuchal measurement
over 2.2 mm and had a median nuchal thickness of 3.1 mm. The results of
this study reinforce the value of a pre-NIPT ultrasound and suggest an
increased risk of chromosomal and structural anomalies in fetuses with
early subcutaneous oedema.
The high incidence of chromosomal and structural abnormalities in cases
of fetal oedema in early pregnancy found in this study also suggests
that in these cases and particularly in those with marked oedema or
hydrops, cell-free DNA testing may not be the ideal screening modality,
despite its high accuracy in detecting the most prevalent trisomies.
Women facing abnormal findings before 11 weeks of gestation should
receive appropriate genetic counselling and may opt for invasive testing
for genetic analysis. Regardless of which investigation method is
chosen, a detailed specialized anatomical assessment of the fetus at 11
to 13+6 weeks is needed, given that a significant
proportion of these cases, with or without chromosomal abnormalities,
will present with structural defects.
The rate of resolution of nuchal oedema at the 11 to
13+6 weeks ultrasound in our series was 81.9%.
Although resolution of increased nuchal thickness before 14 weeks has
been previously described in only one fifth of the fetuses with early
nuchal enlargement, persistence of an increased nuchal translucency has
been consistently associated with adverse outcomes.11