Table 2.

Strategic Considerations for PCR Analysis of Diagnostic Material Biopsied at Different Developmental Stages for Preimplantation Genetic Diagnosis

Stage	Advantages	Disadvantages
Oocyte (1st polar body)	Removal has no effect on embryo development Increased time to perform PCR analysis prior to transfer	Only 1 cell available for analysis Increased risk of diagnostic error Maternally inherited disease only Fewer embryos for transfer (recombination)
Zygote (1st and 2nd polar body)	2 cells for analysis (greater accuracy/reliability) Removal has no effect on embryo development Increased time to perform PCR analysis prior to transfer	Maternally inherited disease only Narrow time window to complete biopsy
Cleavage stage (blastomeres)	Diagnosis of maternally/paternally inherited disorders Large body of clinical data available 2 cells available for analysis (greater accuracy/reliability)	Chromosomal mosaicism present Selection of nucleated blastomere is critical
Blastocyst (trophectoderm)	Sample multiple cells (eliminate PCR failure/ADO) Trophectoderm sampled rather than inner cell mass Embryo quality preselected Higher implantation rate/lower multiple gestation rate	Time for PCR analysis may be limited Cells may not be representative of embryo Fewer embryos for analysis Limited clinical data available