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Since 2004, there have been 11 randomized controlled trials (RCTs) mainly for advanced maternal age (AMA), which have shown no benefit of performing preimplantation genetic screening (PGS). Ten of the RCTs have been performed at the cleavage stage and one at the blastocyst stage. It is probable that the high levels of chromosomal mosaicism at cleavage stages, which may result in the tested cell not being representative of the embryo, and the inability to examine all of the chromosomes using fluorescence in situ hybridization, have contributed to the lack of positive outcome from the RCTs. We suggest that future RCTs should examine alternative biopsy timing (polar body and/or trophectoderm biopsy), and should apply technologies that allow more comprehensive testing to include all chromosomes (microarray-based testing) to determine if PGS shows an improvement in delivery rate. Currently there is no evidence that routine PGS is beneficial for patients with AMA and conclusive data (RCTs) on repeated miscarriage, implantation failure and severe male factor are missing. To evaluate benefits of PGS, an ESHRE trial has recently been started on patients with AMA using polar body biopsy and array-comparative genomic hybridization, which should bring more information on this patient group in the near future.

What next for preimplantation genetic screening (PGS)? A position statement from the ESHRE PGD Consortium steering committee