Preimplantation genetic screening: do we need a degree of caution?

Abstract 

Preimplantation genetic diagnosis (PGD) is a form of very early prenatal diagnosis. The technique combines assisted reproductive technology with molecular and cyto-genetics to allow the identification of abnormalities in embryos prior to implantation. Advancing maternal age is associated with a reduction in oocyte quality due to an increase in meiotic errors, possibly compounded by poor follicular vascularisation, oxidative damage and abnormalities of the meiotic spindle. Screening of preimplantation embryos for aneuploidy (PGS) may ameliorate the effect of female age on reproduction: improving pregnancy rates and decreasing the chance of multiple birth and miscarriage. The technique has been applied to women over the age of 38 years, repeated IVF failure, those with karyotype abnormalities, and those with recurrent miscarriage. The technique has been attractive to and accepted by both patients and clinicians readily. However evidence from trials has been limited by the heterogenous nature of the study populations, the mosaicism of early human preimplantation embryos, the small numbers of embryos produced by these patients, the limited number of fluorescent probes and the cost. Recent well designed prospective randomised controlled trials do not support the routine application of embryo biopsy and screening studies in their current form. It may well be that further refinement of biopsy and genetic analysis in more targeted groups will be required if this invasive and expensive technique is to find its true place.

Keywords: aneuploidy, embryo biopsy, preimplantation genetic screening