Among the many educational materials produced by the European Society of Human Reproduction and Embryology (ESHRE) are guidelines. ESHRE guidelines may be developed for many reasons but their intent is always to promote best quality practices in reproductive medicine. In an era in which preimplantation genetic diagnosis (PGD) has become a reality, we must strive to maintain its efficacy and credibility by offering the safest and most effective treatment available. The dominant motivators for the development of current comprehensive guidelines for best PGD practice were (i) the absence of guidelines and/or regulation for PGD in many countries and (ii) the observation that no consensus exists on many of the clinical and technical aspects of PGD. As a consequence, the ESHRE PGD Consortium undertook to draw up guidelines aimed at giving information, support and guidance to potential, fledgling and established PGD centres. The success of a PGD treatment cycle is the result of great attention to detail. We have strived to provide a similar level of detail in this document and hope that it will assist staff in achieving the best clinical outcome for their patients.
For fertile couples, careful risk assessment and genetic counselling should precede consideration for PGD. Where translocation couples need assisted conception for subfertility, PGD is a valuable screen for imbalance, even when the risk of viable chromosome abnormality is low.
Preimplantation genetic diagnosis (PGD) offers polymerase chain reaction tests for an increasing range of single gene defects, and fluorescence in situ hybridization tests for sex determination (for X-linked conditions) and for aneuploidy detection. Patients carrying chromosome translocations with a high reproductive risk are increasingly seeking to increase their chances of a normal pregnancy with the help of PGD, for which they present a special challenge. This paper describes the behaviour of reciprocal translocations at meiosis, discusses current methods of detecting meiotic outcomes at the preimplantation stage and outlines ways forward for preimplantation diagnosis of these common rearrangements. We also propose a more general strategy using recently developed chromosome-specific sub-telomeric probes, combined, if possible, with proximal probes, to form a strong diagnostic tool.
Multicolour fluorescence in situ hybridisation (FISH) analysis of interphase nuclei in cleavage stage human embryos has highlighted a high incidence of postzygotic chromosomal mosaicism, including both aneuploid and ploidy mosaicism. Indeed, some embryos appear to have a chaotic chromosomal complement in a majority of nuclei, suggesting that cell cycle checkpoints may not operate in early cleavage. Most of these studies, however, have only analysed a limited number of chromosomes (3–5), making it difficult to distinguish FISH artefacts from true aneuploidy. We now report analysis of 11 chromosomes in five sequential hybridisations with standard combinations of two or three probes and minimal loss of hybridisation efficiency. Analysis of a series of arrested human embryos revealed a generally consistent pattern of hybridisation on which was superimposed frequent deletion of one or both chromosomes of a specific pair in two or more nuclei indicating a clonal origin and continued cleavage following chromosome loss. With a binucleate cell in a predominantly triploid XXX embryo, the two nuclei remained attached during preparation and the chaotic diploid/triphoid status of every chromosome analysed was the same for each nucleus. Furthermore, in each hybridisation the signals were distributed as a mirror-image about the plane of attachment, indicating premature decondensation during anaphase consistent with a lack of checkpoint control.
Preimplantation genetic diagnosis (PGD) using fluorescence in situ hybridisation probes was carried out for 59 couples carrying reciprocal translocations. Before treatment, 85% of pregnancies had resulted in spontaneous miscarriage and five couples had achieved a healthy live-birth delivery. Following treatment, 33% of pregnancies failed and 21of 59 couples had a healthy live-born child. The accuracy of diagnosis was 92% (8% false abnormal and 0% false normal results). The overall incidence of 2:2 alternate segregation products was 44%; however, products consistent with 2:2 adjacent segregation were Btwice as likely from male heterozygotes, and those with 3:1 disjunction were three times more likely from female heterozygotes. Our results indicate that up to three stimulation cycles per couple would give an B50% chance of a successful live birth, with the risk of miscarriage reduced to the level found in the general population. In our study, 87% of all normal/balanced embryos available were identified as being suitable for transfer. We conclude that PGD provides benefit for couples with high-risk translocations by reducing the risk of miscarriage and avoiding a pregnancy with an unbalanced form of the translocation; however, for fertile carriers of translocations with a low risk of conceiving a chromosomally unbalanced offspring, natural conception may be a more viable option.
Objective To assess the implications of a change in prenatal diagnosis policy from full karyotype analysis to rapid trisomy testing for women referred primarily for increased risk of Down's Syndrome. Design Retrospective collection and review of data.Setting The four London Regional Genetics Centres.Population Pregnant women (32,674) in the London area having invasive prenatal diagnosis during a six-year three-month period. Methods Abnormal karyotypes and total number of samples referred for raised maternal age, raised risk of Down's Syndrome following serum screening or maternal anxiety were collected. Abnormal karyotypes detected by molecular trisomy detection were removed, leaving cases with residual abnormal karyotypes. These were assessed for their clinical significance. Pregnancy outcomes were ascertained by reviewing patient notes or by contacting obstetricians or general practioners. Main outcome measures Proportion of prenatal samples with abnormal karyotypes that would not have been detected by rapid trisomy testing, and the outcome of those pregnancies with abnormal karyotypes. Results Results from 32,674 samples were identified, of which 24,891 (76.2%) were from women referred primarily for Down's Syndrome testing. There were 118/24,891 (0.47%) abnormal sex chromosome karyotypes. Of the samples with autosomal abnormalities that would not be detected by rapid trisomy testing, 153/24,891 (0.61%) were in pregnancies referred primarily for Down's Syndrome testing. Of these, 98 (0.39%) had a good prognosis (46/98 liveborn, 3/98 terminations, 1/98 intrauterine death, 1/98 miscarriage, 47/98 not ascertained); 37 (0.15%) had an uncertain prognosis (20/37 liveborn, 5/37 terminations; 12/37 not ascertained) and 18 (0.07%) had a poor prognosis (1/18 liveborn, 2/18 miscarriage, 11/18 terminations, 4/18 not ascertained). Conclusions For pregnant women with a raised risk of Down's Syndrome, a change of policy from full karyotype analysis to rapid trisomy testing would result in the failure to detect chromosome abnormalities likely to have serious clinical significance in approximately 0.06% (1 in 1659) cases. However, it should be noted that this figure may be higher (up to 0.12%; 1 in 833) if there were fetal abnormalities in some of the pregnancies in the uncertain prognosis group for which outcome information was not available.
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