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Complete Chromosomal Screening with IVF
Written in Partnership with HRC Fertility, October 8, 2015
Several techniques have been developed to screen the chromosomal DNA of embryos created with IVF. This is commonly referred to as PGS, preimplantation genetic screening; however a better term might be complete chromosomal screening (CCS). PGS determines if an embryo contains the correct number of chromosomes (46,XX for a female and 46,XY for a male), and can identify embryos that have the normal number of chromosomes (euploid) or the abnormal number of chromosomes (aneuploid).
Next Generation Sequencing, the most current iteration of PGS, is a different, deeper way of doing PGS, according to Dr. John Norian. The current PGS techniques use array-CGH which probe each chromosome hundreds of times to determine the proper number of chromosomes. Next Generation Sequencing, as its name implies, uses sequencing instead. It involves biopsying a day-5 embryo (blastocyst), amplifying the DNA and determining euploidy. “We amplify the DNA to determine if there are two copies of each chromosome by sequencing multiple conserved regions of each chromosome,” Norian says.
“The core group of patients I recommend PGS to are women who are at risk for aneuploidy – women who are in their mid-to-high 30s, and particularly low 40s, who are at risk for Down syndrome and other chromosomal errors,” say Norian, a fertility doctor with HRC Fertility in Rancho Cucamonga, CA. " In addition it gives us more information as clinicians, diagnostically, to better understand why people are not getting pregnant.”
HRC Fertility is currently using Next Generation Sequencing for PGS, and Norian is involved with a clinical trial looking at the technology for better selection of embryos with IVF. He’s very excited and optimistic with the preliminary data. “Next Generation Sequencing is going to allow us to be safer as reproductive endocrinologists. It’s going to allow us to put back fewer and healthier embryos; more importantly, to do single embryo transfers while maintaining high pregnancy rates.” According to Norian pregnancy rates of up to 75 percent are being reported.
Next Generation Sequencing in its current iteration requires frozen embryo transfer. “There are arguably benefits to frozen embryo transfer,” Norian says. “So long as you have a good, robust embryology lab that’s very used to freezing, thawing and vitrifying embryos, that’s where you’re going to have the highest success. I think there’s benefit for frozen embryo transfer in that you more closely mimic the natural cycle, at least in terms of the estrogen levels, while not over stimulating the lining.”
Norian says that with PGS and Next Generation Sequencing, “We have much more valuable embryo data and it allows us to put back a single embryo with confidence.”