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The Karolinska Institute, Center for Molecular Medicine, Clinical Genetics Unit and Center for Fetal Medicine, Karolinska University Hospital, Stockholm, Sweden Department of Medical Genetics, Cambridge Institute for Medical Research, University of Cambridge, Cambridge, UK Departments of Obstetrics and Gynecology and Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA *Correspondence to: The-Hung Bui. E-mail: the.bui@karolinska.se All authors contributed equally.

Originally prenatal diagnosis was confined to the diagnosis of metabolic disorders and depended on assaying enzyme levels in amniotic fluid. With the development of recombinant DNA technology, molecular diagnosis became possible for some genetic conditions late in the 1970s. Here we briefly review the history of molecular prenatal diagnostic testing, using Duchenne muscular dystrophy as an example, and describe how over the last 30 years we have moved from offering testing to a few affected individuals using techniques, such as Southern blotting to identify deletions, to more rapid and accurate PCR-based testing which identifies the precise change in dystrophin for a greater number of families. We discuss the potential for safer, earlier prenatal genetic diagnosis using cell free fetal DNA in maternal blood before concluding by speculating on how more recent techniques, such as next generation sequencing, might further impact on the potential for molecular prenatal testing. Progress is not without its challenges, and as cytogenetics and molecular genetics begin to unite into one, we foresee the main challenge will not be in identifying the genetic change, but rather in interpreting its significance, particularly in the prenatal setting where we frequently have no phenotype on which to base interpretation.