Bioethics in Faith and Practice, Volume 4, Number 1

18 The Ethics of IVF the difficult ethical issues around personhood and conception, as polar bodies are not necessary for fertilization or embryonic development, 50 and any selection would occur before fertilization. Polar body biopsy has its limitations, however. Since only the mother’s genetic information is considered, it can only determine oocyte aneuploidy and, in some cases, recessive monogenic diseases. For recessive conditions, the father’s genetic contribution could render the child either homozygously healthy or a heterozygous carrier, but as long as the dominant normal allele from the mother is present, the child should experience minimal ill effects. For dominant Mendelian conditions, however, a normal oocyte cannot guarantee a healthy child, as the father’s allele alone could cause the full effects of the disease. For this reason, other forms of genetic screening are often used instead of or in conjunction with polar body biopsy. Cleavage-stage biopsy allows embryos to grow in vitro for a few days until they reach their third division, when six or more cells are present. One or two cells are then extracted from each embryo for genetic examination. This typically involves polymerase chain reaction (PCR) amplification at the gene of interest followed by fluorescence in situ hybridization (FISH) to identify the presence or absence of a specific sequence. Cleavage-stage biopsy is the most common method of PGD, 51 since it allows direct examination at a variety of loci in the embryo itself, avoiding the major disadvantages of polar body biopsy. However, only one or two cells can be extracted, so accuracy may be compromised by chromosomal mosaicism and PCR sensitivity. There is little consensus on the best number of cells to extract, as extracting more cells gives greater diagnostic accuracy, but may reduce the embryo’s ability to implant and develop normally. 52 Some clinics have begun to increasingly use blastocyst biopsy as an alternative to cleavage-stage biopsy. 53 At this stage, the embryo consists of just over 100 cells, so more cells can be removed. This can lower the risk of PCR failure, which renders no result, or allele dropout, which gives incomplete results. However, only 36-66% of embryos mature this far in vitro. 54 Further, since embryos must be transferred to the womb within 5 or 6 days of extraction, blastocyst biopsy leaves little time for removal and diagnosis. 55 Since cells are removed from the trophectoderm, a portion of the blastocyst that primarily contributes to the formation of placental tissue rather than the developing embryo, blastocyst biopsy is expected to have little effect on embryonic development. 56 In fact, one study found that while cleavage-stage biopsy resulted in a 39% decline in implantation outcomes relative to non-biopsied cells, while blastocyst (trophectoderm) 50 Montag, "Polar Body Biopsy," , 603-607 51 C. Moutou et al., "ESHRE PGD Consortium Data Collection XII: Cycles from January to December 2009 with Pregnancy Follow-Up to October 2010," Human Reproduction 29 (2014), 880-903. 52 Alan Thornhill, Practice Manual of in Vitro Fertilization (New York: Springer, 2012). 53 Niederberger, "Forty Years of IVF," , 185-324 54 G. Kokkali et al., "Blastocyst Biopsy Versus Cleavage Stage Biopsy and Blastocyst Transfer for Preimplantation Genetic Diagnosis of Β-Thalassaemia: A Pilot Study," Human Reproduction 22 (2007), 1443-1449. 55 Sermon, "Preimplantation Genetic Diagnosis," , 1633-1641 56 Kokkali, "Blastocyst Biopsy Versus Cleavage Stage Biopsy and Blastocyst Transfer for Preimplantation Genetic Diagnosis of Β-Thalassaemia: A Pilot Study," , 1443-1449