A genetic abnormality-rather than infertility-may be a reason for a couple to elect IVF. With a known carrier(s) of a speciic genetic disease or a balanced chromosomal rearrangement, PGD may be performed to determine if an oocyte or embryo has the defect. Only embryos without the abnormality would be implanted.
This procedure has numerous applications. It is used to diagnose single-gene disorders such as cystic fibrosis, 3-thalassemia, and hemophilia; to determine gender in X-linked diseases; to identiy mutations such as BRA-J that do not cause disease but confer signiicantly greater later cancer risk; and to match human leukocyte antigens for umbilical cord stem cell transplantation for a sibling (de Wert, 2007; Fragouli, 2007; Grewal, 2004; Rund, 2005; Xu, 2004).
Because typically only one or two cells are available for analysis and because rapid completion time is essential, this procedure is technically challenging. Risks include failure to ampliy the genetic region of interest, selection of a cell that does not contain a nucleus, and maternal cell contamination. Infrequently, afected embryos thought to be normal are implanted, and unaffected embryos are misdiagnosed as abnormal and discarded. Because of this, the American Society for Reproductive Medicine (2008) encourages urther prenatal diagnostic testing-either CVS or amniocentesis-to conirm PGD results.
This term is used for aneuploidy screening that is performed on oocytes or embryos before IVF transfer. Such screening is used with couples who are not known to have or carry a genetic abnormality. Although PGS has obvious theoretical advantages, it has faced challenges in practice.
Mosaicism is common in cleavage-stage embryo blastomeres. However, it may not be clinically signiicant because it often does not relect the actual embryonic chromosomal complement. In addition, among women 35 years or older, pregnancy rates following PGS with FISH are significantly lower than rates observed following IVF without PGS (Mastenbroek, 2007,2011). Because the number of chromosome pairs per cell nucleus that can be evaluated with FISH is limited, more recent eforts have focused on the use of chromosomal comprehensive screening with CMA (Dahdouh, 2015).
Agathokleous M, Chaveeva P, Poon LC, et al: Meta-analysis of second-trimester markers for trisomy 2l. Ultrasound Obstet GynecoIo41(3):247, 2013
Akolekar R, Beta J, Picciarelli G, et al: Procedure-related risk of miscarriage following amniocentesis and chorionic villus sampling: a systematic review and meta-analysis. Ultrasound Obstet GynecoIo45(1):16, 2015
American College of Medical Genetics: Technical standards and guidelines for CFTR mutation testing, 2006. Available at: https:!lwww.acmg.net/Pagesl ACMG_Activitieslstds-2002/cf.htm. Accessed December 30, 20o16
American College of Obstetricians and Gynecologists: Hemoglobinopathies in pregnancy. Practice Bulletin No. 78, January 2007, Reairmed 2015
American College of Obstetricians and Gynecologists: Neural tube defects. Practice Bulletin No. 44, July 2003, Reairmed 2016a
American College of Obstetricians and Gynecologists: Prenatal diagnostic testing for genetic disorders. Practice Bulletin No. 162, May 2016b