From karyotyping to array-CGH in prenatal diagnosis

Conventional karyotyping detects chromosomal anomalies in up to 35% of pregnancies with fetal ultrasound anomalies, depending on the number and type of these anomalies. Extensive experience gained in the past decades has shown that prenatal karyotyping is a robust technique which can detect the majority of germline chromosomal anomalies. For most of these anomalies the phenotype is known. In postnatal diagnosis of patients with congenital anomalies and intellectual disability, array-CGH/SNP array has become the first-tier investigation. The higher abnormality detection yield and its amenability to automation renders array-CGH also suitable for prenatal diagnosis. As both findings of unclear significance and unexpected findings may be detected, studies on the outcome of array-CGH in prenatal diagnosis were initially performed retrospectively. Recently, prospective application of array-CGH in pregnancies with ultrasound anomalies, and to a lesser extent in pregnancies referred for other reasons, was studied. Array-CGH showed an increased diagnostic yield compared to karyotyping, varying from 1-5%, depending on the reason for referral. Knowledge of the spectrum of array-CGH anomalies detected in the prenatal setting will increase rapidly in the years to come, thus facilitating pre- and posttest counseling. Meanwhile, new techniques like non-invasive prenatal diagnosis are emerging and will claim their place. In this review, we summarize the outcome of studies on prenatal array-CGH, the clinical relevance of differences in detection rate and range as compared to standard karyotyping, and reflect on the future integration of new molecular techniques in the workflow of prenatal diagnosis.