Reproductive Genetics

Preconception Carrier Screening and Prenatal Screening 

While most babies a born healthy, about 3 percent of newborns have a major birth defect. Preconception screening and testing can help a couple decide whether or not to have children, and allows them to consider all of their reproductive options. It also greatly minimizes the potential risks, some of them life-threatening, to a mother and fetus. (44) 

The advancement of DNA sequencing technologies has enabled the development of more advanced screening techniques, as faster next generation technology no longer keeps doctors waiting for their results. New DNA sequencing technologies are ever improving, furthering the development of preconception carrier screening and prenatal screening.

As a result of the genomic carrier screening programs, the incidence of inherited conditions, such as Tay-Sachs disease (TSD), has decreased by more than 90 percent.

Since many individuals who are carriers of genetic disorders don't have symptoms, primary care physicians can play an important role in determining if carrier screening and testing are appropriate. (44) Recent advances in technology now allow for genetic carrier screening to be performed for many genetic disorders at one time for a relatively low cost. There are many testing panels available for genetic screening, called by a number of names, including ‘multi-disease genetic carrier screening panel’, ‘universal genetic carrier screening’, or ‘all-in-one genetic carrier screening.

Figure (45) 

Non-Invasive Prenatal Testing  

The aim of non-invasive prenatal testing (NIPD) is to obtain diagnostic information about a pregnancy without causing harm to the unborn child. In the 1990's, researchers discovered fetal DNA within the circulation of pregnant women which offered a promise of someday using a simple blood draw to diagnose genetic conditions and chromosome disorders during a pregnancy. (37)

The main challenge to non-invasive prenatal testing (NIPD) is the very small amount of fetal DNA that is present in maternal circulation. Natera's Parental Support technology specializes in testing small quantities of DNA, including traces of fetal DNA found in maternal blood during pregnancy. Natera now provides non-invasive prenatal paternity testing and is sponsoring a clinical trial for non-invasive prenatal detection (NIPD) of chromosomal abnormalities. (38)

Figure (38) 


Figure (42) 

Currently, amniocentesis or CVS are the procedures to diagnose  genetic conditions or confirmation of paternity during a pregnancy . These procedures are considered invasive and carry a slight risk for miscarriage. Fetal cells are obtained by removal of a small amount of fluid from the pregnant uterus in second trimester of the pregnancy.  These cells are then harvested and for further genetic studies including chromosome analysis, single gene tests  and more recently whole genome arrays. (43)


Preimplantation Genetic Diagnosis 

PGD is for patients who are at serious risk of delivering babies with specific genetic diseases such as cystic fibrosis, Tay-Sachs disease, or sickle cell anemia, or for women who may have aneuploidy, or the wrong number of chromosomes in their embryos. A baby with the wrong number of chromosomes typically is lost through miscarriage. PGD has enabled many patients referred to the center to deliver healthy babies. (40)

If  fresh transfer is planned, Day 3 biopsy is performed. One cell is removed from each available embryo on Day 3 after fertilization and sent for genetic testing. Results are made available to the IVF center the morning of Day 5 in time for a fresh transfer that day. 

In Day 5 biopsy, a cluster of two to ten cells is removed from the mass of cells called the trophectoderm, which is the tissue that will become the placenta. Since embryos do not survive well outside of the mother’s uterus beyond Day 5 or 6, the embryos are frozen until results become available (5 days from receipt of cells). Embryos with normal chromosome results may then be thawed and transferred. (35)

Location of the embryo from day 0 - day 9 Figure (36)
             Day 3 Biopsy            Figure (35)            Day 5 Biopsy

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