INTRODUCTION
Since the clinical implementation of non-invasive prenatal testing
(NIPT) by cell-free DNA analysis of maternal blood, the test has been
incorporated in prenatal care as a safe and accurate method for the
detection of common chromosomal abnormalities. While there are many
advantages to NIPT, the most significant is its high accuracy in
screening for trisomies 21, 18 and 13 with a detection rate of 99% for
T21, and low false-positive rate of less than 0.1%.1
In its most recent guidelines on NIPT, the International Society of
Ultrasound in Obstetrics and Gynecology stated that all pregnant women
should be offered a first trimester ultrasound regardless of their
intention to undergo cell-free DNA screening.2However, there are no established guidelines or pathways around
incorporating an early pre-test ultrasound in current clinical practice.
In a recent study of 2,337 women who underwent an ultrasound between 10
and 14 weeks of gestation, 16.1% had an unexpected finding detected on
the pre-NIPT scan. These findings altered the clinical management for
the patients involved.3
As a tertiary ultrasound unit our current model of care for NIPT is to
offer a pre-test scan between 9 and 10+6 weeks of
gestation and post-test genetic counselling. This scan provides an
opportunity to confirm viability, establish gestational age and identify
miscarriage, multiple pregnancy or early twin demise, all of which can
affect the choice of the first trimester aneuploidy screening method.
This creates an opportunity for early assessment of the fetus.
While the implications of increased nuchal translucency measurement (NT)
at the 11 to 13+6 weeks scan (crown rump length
[CRL] between 45 mm-84 mm) and its association with aneuploidy and
structural defects is well established4, the
implications of increased nuchal translucency measurement at CRL ≤ 44 mm
is unclear.
Fetal oedema at the pre-NIPT scan is a potential early marker for both
structural and chromosomal anomalies. However, in the absence of any
evidence-based guidelines this finding presents challenges in both the
counselling and management of pregnant women seeking aneuploidy
screening. In a prospective cohort study, Grande et al .
constructed a reference range for NT in fetuses with CRL between 28-44
mm and concluded that an increased NT at this early gestation appeared
to be an effective marker for the common
aneuploidies.5 The objective of this study is to
investigate the incidence of structural and chromosomal abnormalities in
cases of reported fetal oedema on early ultrasound conducted before
NIPT.