RESEARCH – December 2021

A two-year study assessing the performance of combined first trimester screening for chromosomal disease in Estonia

Authors: Konstantin Ridnõi, Kai Muru, Eva-Liina Ustav, Pille Tammur, Triin Mölter-Väär, Karin Asser, Ferenc Szirko, Tiia Reimand, Katrin Õunap

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Background. Combined first trimester screening (cFTS) has been used in Estonia for more than ten years in combination with second trimester serum screening. From 2016 cFTS has become primary screening test for fetal chromosomal disease in Estonia, according to the national prenatal diagnostics guideline. We conducted a two-year prospective study (2017-2018) to assess the effectiveness of cFTS in two major Estonian hospitals.
Methods. A study-group of cFTS consisted of 14,566 women with singleton pregnancies, attending cFTS to East-Tallinn Central Hospital and Tartu University Hospital. Screening was performed according to national guideline protocol.
Results. We performed cFTS in 14,566 women with singleton pregnancies. Screen-positive rate was 3.54%. Prenatal detection rate in first trimester was 94% (95CI 84.09%-97.98%) for trisomy 21 and 100% for trisomies 18 (95CI 95CI 74.12%-100%) and 13 (95CI 95CI 43.85-100%) . False-positive rate was 3.12%. Screening sensitivity was 95.38% (95CI 86.24%-98.80%), specificity was 96.86% (95CI 96.56%- 97.13%), positive predictive value 11.99% (95CI 9.38%-15.18%), negative predictive value 99.97% (95CI 99.93%-99.99%).
Conclusions. cFTS is an effective method for prenatal screening of chromosomal disease. The detection rate for trisomy 21 was higher compared to previously published Estonian study. The switch to cFTS in Estonia was justified.