EP18.13: Can combining second trimester quadruple test with mid‐trimester anomaly scan for soft markers and defects improve detection of chromosomal anomalies?

To assess detection of chromosomal anomalies combining quadruple marker test with anomaly scan in second trimester for soft markers and fetal defects. This is a retrospective study of the data from a tertiary fetal care centre in South India from 2012 to 2023. Pregnancies with second trimester quadruple test and anomaly scan between 16 and 20 weeks by FMF certified operators were included. The data is stored in an Astraia database. Quadruple test performed on Perkin Elmer divided into high risk (>1:250), intermediate risk (1 in 251–1 in 999), low risk (<1 in 1000). Outcomes confirmed by prenatal testing if performed, telephonic interview with parents confirming absence of any neurodevelopmental delay and examination of hospital delivery records excluding terminations, miscarriages, IUDs without known karyotype were analysed. 52/1742 (2.9%) have structural defects. Of 3/12 (25%) in high risk, 2 had T21 and 1 had Turners, of 1/9 (11.1%) in intermediate group 1 had T18, of 1/31 (3.2%) in low risk group 1 had T18. 321/1742 (18.4%) have soft marker(s). Of 2/47 (7.4%) in high risk, 2 had T21. Of 1/37 (2.7%) in intermediate group, 1 had Turners. 0/237 in low risk group had a chromosomal anomaly. 1369/1742 (78.5%) had no structural defects nor soft markers. Of 2/253 (0.7%) in high risk group 1 had Klinefelters on prenatal testing and 1 had T21 detected in postnatal period who declined invasive testing. None found in intermediate and low-risk groups. Our study confirms that combining second trimester quadruple test with genetic sonogram complements each other. Invasive testing only on high risk group (>1 in 250) and structural defects misses 1 Turner syndrome. Relying solely on anomaly scan misses 2 high-risk quadruple chromosomal anomalies. Our protocol includes risk readjustment of quadruple test after anomaly scan as this improves detection rate and avoids unnecessary invasive testing. If there are fetal defects and/or markers then invasive testing is offered, irrespective of risk category.