Introduction
In 1997, Lo et al. discovered that cell-free fetal DNA (cffDNA) found in
maternal plasma was a potential material for fetal aneuploidy analysis
[1]. With the development of next-generation sequencing
technologies, cell-free DNA screening (cfDNA screening) using cffDNA was
clinically available in the United States since 2011 and in Korea since
2016. Since cfDNA screening has a sensitivity higher than 99% with a
false-positive rate of less than 0.1% for detecting T21 [2-3], its
performance is better than that of traditional aneuploidy screening
tests. The clinical implementation of cfDNA screening has rapidly
altered prenatal screening strategy and the timing of prenatal screening
has shifted to earlier gestational weeks.
Nuchal translucency (NT) is an important parameter for first trimester
aneuploidy screening. The association of increased nuchal translucency
(INT) and chromosomal abnormalities was first known in 1992 [4]. INT
is associated with adverse pregnancy outcomes such as fetal cardiac
defects, miscarriage, and low birth weight, as well as chromosomal
abnormalities [5-7]. However, the significance of NT measurements
for aneuploidy screening has declined since the introduction of cfDNA
screening. The American College of Obstetricians and Gynecologists
(ACOG) and the Society for Maternal-Fetal Medicine (SMFM) (2016)
guidelines recommend cfDNA screening or diagnostic tests when NT is
greater than 3mm or more than 99th percentile if there
is no structural abnormality of the fetus. However, it is doubtful
whether a diagnostic test is needed in cases with NT between
95th and 99th percentile.
The purpose of this study was to evaluate the clinical usefulness of
cfDNA screening in cases with NT between 95th and
99th percentile