Accreditation according to an internationally recognized standard is increasingly acknowledged as the single most effective route to comprehensive laboratory quality assurance, and many countries are progressively moving towards compulsory accreditation of medical testing laboratories. The ESHRE PGD Consortium and some regulatory bodies recommend that all PGD laboratories should be accredited or working actively towards accreditation, according to the internationally recognized standard ISO 15189, 'Medical laboratories-Particular requirements for quality and competence'. ISO 15189 requires comprehensive quality assurance. Detailed management and technical requirements are defined in the two major chapters. The management requirements address quality management including the quality policy and manual, document control, non-conformities and corrective actions, continual improvement, auditing, management review, contracts, referrals and resolution of complaints. Technical requirements include personnel competence (both technical and medical), equipment, accommodation and environment, and pre-analytical, analytical and post-analytical processes. Emphasis is placed on the particular requirements of patient care: notably sample identification and traceability, test validation and interpretation and reporting of results. Quality indicators must be developed to monitor contributions to patient care and continual improvement. We discuss the implementation of ISO 15189 with a specific emphasis on the PGD laboratory, highlight elements of particular importance or difficulty and provide suggestions of effective and efficient ways to obtain accreditation. The focus is on the European environment although the principles are globally applicable.

The aim of PGD is to test the preimplantation embryo for specific conditions for couples at risk of transmitting that genetic abnormality to their offspring.The couple need to go through IVF procedures to generate embryos in vitro.The embryos can be biopsied at either the zygote, cleavage or blastocyst stage. PGS uses the same technology to screen for chromosome abnormalities in embryos from patients going through IVF procedures as a method of embryo selection. Chromosome analysis was originally performed using fluorescent in situ hybridisation (FISH) which has now been replaced by array comparative genomic hybridisation or next generation sequencing (NGS) For the diagnosis of single gene defects, the polymerase chain reaction (PCR) has been used and has become highly developed over the years. More recently, SNP arrays and karyomapping have been introduced. PGD/PGS require partnership between IVF laboratories and diagnostic centres. As diagnosis can be performed using a variety of strategies with different technologies, accreditation of PGD diagnostic laboratories is important. Accreditation gives IVF centres an assurance that the diagnostic tests conform to specified standards. ISO 15189 is an international laboratory standard specific for medical laboratories. A requirement for accreditation is to participate in external quality assessment schemes Key wordsQuality control, Preimplantation genetic diagnosis 3 The current status of PGD and PGSInitial clinical application of PGD PGD was first performed in 1989 and since this time, genetic testing has seen major advances. PGD was developed as an alternative to prenatal diagnosis, for couples at risk of transmitting a genetic abnormality to their children.Couples have to go through IVF procedures to generate embryos in vitro, even though many of the couples that go through PGD are fertile. The embryos can be biopsied by the embryologists at the zygote stage (removal of the first and second polar body), cleavage stage (removal of 1-2 blastomeres from the 6-8 cell embryo) and blastocyst stage (removal of some trophectoderm cells) (Harton et al., 2011a). Up until recently, almost all PGD cycles were performed on blastomeres after cleavage stage biopsy (Harper et al, 2012, Moutou et al, 2014, but numerous studies have found that cleavage stage embryos exhibit high levels of chromosomal mosaicism, which means that biopsied cells may not be representative of the rest of the embryo (Harper et al, 1995, Munne et al, 1995, Fragouli et al, 2011, Taylor et al, 2014a. This is especially important when trying to perform PGD for a chromosome abnormality. Polar body biopsy is rarely used as it only gives genetic information on the maternal genome. In recent years, the IVF community have seen an increase in the use of blastocyst transfer (Glujovsky et al, 2012) and this has been reflected in the increased use of blastocyst biopsy for PGD (Moutou et al, 2014).The genetic testing should be performed by a specialised genetic testing laboratory. The very first cases of PGD wer...

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