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