Polar body based aneuploidy screening is poorly predictive of embryo ploidy and reproductive potential

Abstract

PurposePolar body (polar body) biopsy represents one possible solution to performing comprehensive chromosome screening (CCS). This study adds to what is known about the predictive value of polar body based testing for the genetic status of the resulting embryo, but more importantly, provides the first evaluation of the predictive value for actual clinical outcomes after embryo transfer.MethodsSNP array was performed on first polar body, second polar body, and either a blastomere or trophectoderm biopsy, or the entire arrested embryo. Concordance of the polar body-based prediction with the observed diagnoses in the embryos was assessed. In addition, the predictive value of the polar body -based diagnosis for the specific clinical outcome of transferred embryos was evaluated through the use of DNA fingerprinting to track individual embryos.ResultsThere were 459 embryos analyzed from 96 patients with a mean maternal age of 35.3. The polar body-based predictive value for the embryo based diagnosis was 70.3 %. The blastocyst implantation predictive value of a euploid trophectoderm was higher than from euploid polar bodies (51 % versus 40 %). The cleavage stage embryo implantation predictive value of a euploid blastomere was also higher than from euploid polar bodies (31 % versus 22 %).ConclusionPolar body based aneuploidy screening results were less predictive of actual clinical outcomes than direct embryo assessment and may not be adequate to improve sustained implantation rates. In nearly one-third of cases the polar body based analysis failed to predict the ploidy of the embryo. This imprecision may hinder efforts for polar body based CCS to improve IVF clinical outcomes.

Oocyte competency is the key to embryo potential

“…Intriguingly, they also found a higher contribution of metaphase II errors to embryo aneuploidy than previously reported. Some oocytes with aneuploid PBs, however, can go on to produce euploid embryos (56,61). The mechanism underlying this self-correction mechanism is not understood, but the ability of nondisjunction occurring during meiosis to correct during later preimplantation development reduces the specificity of PGS in PBs.…”

Technique to ‘Map' Chromosomal Mosaicism at the Blastocyst Stage

“…This would suggest that the error arose during mitosis and not meiosis. Previous research has demonstrated that ∼ 25% of polar bodies are aneuploid [Salvaggio et al, 2014], while ∼ 50% of blastocysts are aneuploid [Taylor et al, 2014b, c]. The higher incidence of aneuploidy at the blastocyst stage suggests that a majority of aneuploidy may be mitotic in origin.…”

Recent advances in preimplantation genetic diagnosis

“…1 Although polar body biopsy is less invasive, it is less predictive of actual clinical outcome than direct embryo assessment. 2 Genetic laboratories have developed their own protocols to perform different molecular tests on the limited amount of DNA obtained from biopsy. Traditionally, fluorescent in-situ hybridisation is used for cytogenetic diagnosis, and polymerase chain reaction for molecular diagnosis.…”