Ultrasound Markers of Chromosomal Abnormalities in the First and Second Trimester: Hard and Soft Signs, Strategy
First Trimester Screening (11–14 weeks)
According to the ISUOG Practice Guidelines for performing the 11–14 week scan, first-trimester screening for trisomy 21 is based on a combination of maternal age, nuchal translucency thickness, and additional ultrasound markers — assessment of the ductus venosus and tricuspid regurgitation (Wagner et al., 2017; Huggon et al., 2003).
Measurement of the ductus venosus pulsatility index reduces the rate of false-positive results in first-trimester screening (Timmerman et al.). Tricuspid regurgitation is considered a marker of chromosomal abnormalities in the fetus at 11–14 weeks (Huggon et al., Heart 2003).
Combined Test
The first-trimester combined test is used for screening trisomies 21, 18, and 13 (Santorum et al., 2016; Malone et al., 2005). According to ACR–ACOG–AIUM–SMFM–SRU (2023), screening can be performed in the first or second trimester or both.
Structural (Hard) Signs on the 11–14 Week Scan
The detection of structural anomalies on the 11–14 week scan is significant alongside aneuploidy markers (Grande et al., 2012). Major structural defects can be detected as early as the first trimester in an unselected population (Novotna et al., 2012; Pilalis et al., 2012). Ultrasound findings serve as a basis for referral for prenatal cytogenetic testing (Hanna et al., 1996).
Strategy for Detected Markers
Upon detection of structural anomalies, prenatal genetic testing is recommended, including exome sequencing for structural defects identified by ultrasound (PAGE, Lord et al., Lancet 2019). Bet et al. (2024) recommend performing anomaly scans in the first and second trimester in a fetal medicine unit.
Features in Multiple Pregnancies
According to ISUOG (role of ultrasound in twin pregnancy, 2025), in screening trisomies by cfDNA in twins, there are factors affecting test failure (Galeva et al., 2019). Determination of chorionicity by the lambda sign is performed in the first trimester (Maruotti et al., 2016).
Frequently asked questions
What ultrasound markers are used in the 11–14 week screening?
Nuchal translucency (NT) thickness, as well as assessment of the ductus venosus and tricuspid regurgitation in combination with maternal age (ISUOG, 2023).
How to reduce the rate of false-positive results?
Measurement of the ductus venosus pulsatility index reduces the rate of false-positive results in first-trimester screening (Timmerman et al.).
Which trisomies is the first-trimester combined test designed for?
For trisomies 21, 18, and 13 (Santorum et al., 2016).
What to do if a structural anomaly is detected on the 11–14 week scan?
Refer for prenatal cytogenetic testing; exome sequencing is possible for structural defects (PAGE, Lord et al., 2019). Scanning is recommended in a fetal medicine unit (Bet et al., 2024).
Where is it recommended to conduct anomaly screening in the first and second trimester?
Bet et al. (2024) recommend always performing anomaly scans in the first and second trimester in a fetal medicine unit.