Pre-implantation Genetic Diagnosis

Giving birth to a healthy child is more important than just having a child for couples. In this regard, recent advancements in diagnosis and treatment of genetic diseases are pivotal. Preimplantation genetic diagnosis (genetic analysis carried out before embryo is transferred to the uterus) enables early diagnosis of genetic diseases. Ending life of a living fetus with curettage due to a disease is a source of sorrow for both the doctor and the parent.

Healthy Babies Can Be Obtained

To have couples with carrier status of a genetic disease give birth to a healthy baby, embryos obtained through in vitro fertilization or microinjection are evaluated and healthy embryos are selected and transferred. Here, the aim is to prevent transmission of chromosomal anomalies, reduce risk of miscarriage and select genetically healthy embryos. Recently, pregnancies are achieved through transfer of embryos into the uterus following genetic analysis. Preimplantation genetic diagnosis may prevent death of newborn infant due to any disease that may emerge at the birth or in the future and thus, couples with carrier status of a genetic disease may give birth to a healthy child.

It is especially preferred in IVF patients with history of recurrent failure of implantation, advanced maternal age, recurrent miscarriage and presence of translocation as well as past obstetric history of aneuploidy in previous pregnancies. Moreover, tissue-compatible and healthy embryos can be selected that are healthy regarding a documented single-gene disease for women or men who have the disease.

Novel Methods Used for Preimplantation Genetic Diagnosis

Preimplantation Genetic Diagnosis has been used for approximately two decades and five chromosomes (13, 18, 21, X, Y or 13, 16, 18, 21, 22) were analyzed with FISH method in the preliminary phases of its evolution, but the figure is, now, 9 chromosomes. Recently, 24 chromosomes can be analyzed using Microarray (aCGH) technology and it is immediately followed by NGS technique that gained popularity quickly for in vitro fertilization therapies as of 2015.

What Are Advantages of Next Generation Sequencing (NGS)?

NGS is the abbreviation for Next Generation Sequencing which is a novel genetic analysis method used to screen 24 chromosomes in embryos. NGS is deemed a revolutionary DNA sequencing technology in the field of genetic research; it allows both numeric and structural analysis and sequencing of whole human genome within a very short period of time – one day. NGS can identify mosaic embryos better relative to other PGD techniques. Besides the ability to screen a very large locus of gene both numerically and structurally, other advantages include low error margin, more accurate results, quicker access to results and lower cost. Moreover, this method can combine analysis of single-gene diseases, HLA typing and screening of 24 chromosomes.

How is PGD Performed?

Preimplantation genetic diagnosis starts with intracytoplasmic sperm injection that implies meeting the egg of mother with sperm of father outside the body. When embryos reach Blastocyst phase on day 5 to 6 of development, several cells are biopsied without any damage to embryo; these cells are sent to genetic laboratory for 24-chromosome screening, while embryos are frozen. The risk of damage to embryo is very low, if this procedure is performed by an experienced embryologist. Embryo(s) with healthy genetic structure, as verified by this analysis, are transferred, after uterine cavity is prepared for implantation, and thus, higher conception rates can be obtained.