Genetic evaluation for twin pregnancies using karyotyping and single nucleotide polymorphism array analysis

•Aneuploidies are the primary anomalies in twin pregnancies.•Fetuses in DCDA pregnancies are more susceptible to pathogenic or likely pathogenic submicroscopic aberrations compared to those in MCDA pregnancies.•Cardiac defects and elevated NT in twin pregnancies emerged as two strongly correlated indicators of chromosomal abnormalities, particularly in the context of DCDA pregnancies. The study aimed to assess chromosomal abnormalities in twin pregnancies using karyotyping and SNP array analysis. The research involved 530 twin pregnancies from two prenatal diagnosis centers between October 2012 and October 2022. Two types of twin pregnancies were considered: monochorionic diamniotic (MCDA) and dichorionic diamniotic (DCDA), with a total of 177 MCDA and 353 DCDA cases. Chromosomal abnormalities were examined based on chorionic and amniotic sac properties and clinical indications. Among 42 twin pregnancies, 50 fetuses showed chromosomal abnormalities by karyotyping, with 35 cases of aneuploidy in DCDA and 10 in MCDA. Trisomy 21 was the most common aberration, affecting 15 fetuses in DCDA and 4 in MCDA. The rate of discordant karyotypes in MCDA and DCDA groups was 1.1% and 8.8%, respectively. Ultrasound abnormalities and advanced maternal age were frequent indications (55.3% and 39.2%, respectively). Aneuploidy frequencies in DCDA and MCDA pregnancies with advanced maternal age were 10.6% and 4.5%. Cardiac defects and increased nuchal translucency were common anomalies, with higher incidences of chromosomal abnormalities in DCDA (12.5% and 6.9%) and MCDA groups (23.5% and 3.7%). SNP array identified 1.6% clinically significant copy number variants in DCDA fetuses with ultrasound abnormalities, while no significant CNVs were found in MCDA pregnancies. Chromosomal aneuploidies were the primary abnormalities in twin pregnancies, with detectable abnormalities and clinically significant CNVs more likely in DCDA pregnancies, especially those with ultrasound abnormalities.