Detection of fetal abnormalities by second-trimester ultrasound screening in a non-selected population.

INTRODUCTION: This study assessed the sensitivity of routine ultrasound examination for the detection of abnormal chromosomes and structural malformations in fetuses in the second trimester in a non-selected population.

MATERIAL AND METHODS: Prenatal diagnoses of fetal abnormalities in 10 414 fetuses and newborns were reviewed and compared with all postnatal diagnoses of congenital abnormalities between 2006 and 2013.

RESULTS: Overall, 243 fetuses and newborns had confirmed congenital abnormalities, with a prevalence of 2.3%. Of these fetuses and newborns, 23% (56/243) had chromosomal abnormalities (overall prevalence 0.5%), and 77% (187/243) had normal chromosomes with either major (44%; 82/187) or minor (56%; 105/187) structural malformations (overall prevalence 1.8%). One hundred and seven abnormalities were detected prenatally, yielding a total sensitivity for prenatal detection of fetal abnormalities of 44.0% (107/243; 95% CI 37.8-50.2), with specificity of 99.9%, a positive predictive value of 94.7%, and a negative predictive value of 98.7%. The sensitivity for prenatal detection before 22 weeks of gestation was 40.3% (98/243; 95% CI 34.1-46.5). The prenatal detection rate of chromosomal abnormalities was 60.7% (34/56) and, for structural malformations, was 39.0% (73/187).

CONCLUSIONS: In a routine clinical setting at a county hospital with a non-selected population, half of the major structural malformations in chromosomally normal fetuses are detected by routine ultrasound examination in the second trimester. Chromosomal abnormalities have the highest probability for prenatal detection; the majority are diagnosed by amniocentesis before the routine ultrasound examination in high-risk women.