Authors: Catherine Marin DeUgarte, Man Li, David Hill, Hal Danzer, Mark Surrey
Background: In vitro fertilization success rates have increased with improvements in laboratory techniques. Preimplantation genetic diagnosis (PGD) has improved embryo selection by allowing the option to eliminate embryos with chromosomal abnormalities. Most embryos have an even number of cells as would be expected from normal cell division. We hypothesized that an odd number of cells might confer a higher probability of chromosomal abnormalities.
Purpose: The purpose of this study was to determine 1) the frequency of embryos with an odd-number of cells and 2) to evaluate whether odd-number cell embryos are associated with more PGD abnormalities.
Materials and Methods: Embryos from patients that underwent PGD at ART (Assisted Reproductive Technologies) from January through June 2003 were analyzed retrospectively. A total of 626 embryos were obtained from 92 women (mean age 38). Cell number and embryo-grade were documented at the time of the blastomere biopsy for PGD (day 3 after oocyte retrieval). PGD analysis was done for the following chromosomes: 13, 18, 21, X and Y. Results from PGD analysis were reported as normal female, normal male, abnormal female, abnormal male, and inconclusive. The embryo cell-number was compared with the results of PGD. Statistical analysis was performed using the χ2 test.
Results: The results of PGD were inconclusive for chromosomal abnormalities, and therefore excluded in a total of 77 of 626 embryos (12%). Of the remaining embryos that were analyzed, 99 (19%) were odd-numbered (3,5,7, or 9 cells) and 450 (81%) were even-numbered (2,4,6,8,10,12, or 14 cells). No significant difference was noted in those embryos having chromosomal abnormalities between the odd-number cell and even-number cell groups (49% and 43% respectively). Similarly, no significant difference was noted between the groups for embryos without detectable chromosomal abnormalities or labeled as normal (50.5% vs. 57 %).
Conclusion: In this study, a minority of embryos had an odd-number of cells (19%). The presence of an odd-number of cells was not helpful in predicting an abnormality in the five chromosomes tested using PGD. While not statistically significant, a higher percentage of embryos with even-cell number were noted to be normal by PGD.