Chromosomal abnormalities detected by karyotyping and microarray analysis in twins with structural anomalies

Area of Science:

• Perinatology
• Medical Genetics
• Prenatal Diagnosis

Background:

• Twin pregnancies with structural anomalies require accurate cytogenetic evaluation.
• Chorionicity and amnionicity influence the risk of chromosomal abnormalities in affected twins.
• The utility of chromosomal microarray analysis (CMA) in this population needs further assessment.

Purpose of the Study:

• To determine the incidence and types of chromosomal abnormalities in twins with structural anomalies.
• To compare the distribution of these abnormalities based on chorionicity, amnionicity, and anomaly type.
• To evaluate the added diagnostic value of CMA compared to conventional karyotyping in twins.

Main Methods:

• Retrospective analysis of 534 twin pregnancies with fetal structural anomalies over 11 years.
• Categorization of twin pregnancies into monochorionic monoamniotic (MCMA), monochorionic diamniotic (MCDA), and dichorionic diamniotic (DCDA).
• Analysis of cytogenetic results from karyotyping and/or CMA in relation to chorionicity, amnionicity, and anomaly type.

Main Results:

• Dichorionic diamniotic (DCDA) twins showed a higher incidence of chromosomal abnormalities (25.4%) and aneuploidies (22.8%) compared to MCMA (3.7%) and MCDA (15.3%) twins.
• Specific structural anomaly types were more frequently associated with chromosomal abnormalities in DCDA twins.
• Hydrops fetalis was linked to the highest abnormality rate, with Turner syndrome (45,X) in 67.6% of affected fetuses; CMA identified pathogenic copy-number variations (CNVs) in 2.0% of DCDA fetuses.

Conclusions:

• Dichorionic twins with structural anomalies have a significantly higher risk of chromosomal abnormalities, particularly aneuploidies, than monochorionic twins.
• The incremental diagnostic yield of CMA over karyotyping in twin pregnancies with structural anomalies appears lower than in singleton pregnancies.
• Risk stratification based on chorionicity is crucial for genetic counseling in twin pregnancies with fetal structural anomalies.