Embryos whose polar bodies contain isolated reciprocal chromosome aneuploidy are almost always euploid.

study questionWhen a chromosome aneuploidy is detected in the first polar body and a reciprocal loss or gain of the same chromosome is detected in the second polar body, is the resulting embryo usually aneuploid for that chromosome? SUMMARY ANSWER: When reciprocal aneuploidy occurs in polar bodies, the resulting embryo is usually normal for that chromosome, indicating that premature separation of sister chromatids (PSSC)-not non-disjunction-likely occurred in meiosis I. WHAT IS KNOWN ALREADY: Single-nucleotide polymorphism-based microarray analysis can be used to accurately determine the chromosomal status of polar bodies and embryos. Sometimes, the only abnormality found is a reciprocal gain or loss of one or two chromosomes in the two polar bodies. Prediction of the status of the resulting embryo in these cases is problematic. STUDY DESIGN, SIZE, DURATION: Blinded microarray analysis of previously diagnosed aneuploid embryos that had reciprocal polar body aneuploidy. MATERIALS, SETTING,

methodsIVF cycles were performed between 2008 and 2011 in patients aged 40 ± 3 years (range 35-47 years) with an indication for polar body-based aneuploidy screening. Thirty-five aneuploid vitrified Day 3 embryos were warmed, cultured to Day 5 and biopsied for microarray analysis. Predictions were made for the ploidy status of the embryo if PSSC or non-disjunction had occurred. The signal intensity for the aneuploid chromosome in the first polar body was compared between those that resulted in euploid and aneuploid embryos. MAIN RESULTS AND THE ROLE OF CHANCE: Among 34 embryos with evaluable results, 31 were euploid on re-analysis. Of 43 chromosomes that had reciprocal aneuploidy in the polar bodies, 41 were disomic in the embryo, indicating that PSSC was likely to have occurred 95% (95% confidence interval 85-99%) of the time. The log 2 ratio signal intensity from the chromosomes that underwent non-disjunction, resulting in unbalanced embryos, were outliers when compared with those that underwent PSSC. LIMITATIONS, REASONS FOR CAUTION: Although most embryos with reciprocal aneuploid polar bodies were euploid, it is unknown whether they maintain equivalent reproductive potential when transferred. Further study is needed to determine whether these embryos should be re-biopsied and considered for transfer. WIDER IMPLICATIONS OF THE

findingsThis study is consistent with increasing evidence that PSSC is the primary cause of meiosis I errors in embryos from women of advanced reproductive age. Clinicians should be cautious in interpreting results from polar body aneuploidy screening, especially when only the first polar body is tested.