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The following terms are helpful in understanding the various tests used for fertility issues and testing during pregnancy.
24 chromosome screening

Another term for Preimplantation Genetic Screening (PGS); a procedure that screens all 24 chromosomes in embryos to ensure there are the correct number.


An allele is one of two or more forms of the DNA sequence of a particular gene. Different DNA sequences (alleles) can result in different traits, such as color of skin, hair or eyes. If both alleles are the same, the person is termed a homozygote. If the alleles are different, the person is a heterozygote.


An invasive procedure where a needle is used to extract a small amount of fluid from the amniotic sac surrounding the developing fetus. Used for prenatal testing, typically in between the 16th to 20th week of pregnancy, this procedure is associated with a small risk of miscarriage.


An embryo with an abnormal number of chromosomes.

Aneuploidy screening

Another term for PGS; the procedure of screening chromosomes in embryos to determine if they have the correct number of chromosomes.


Autosomes are any of the chromosomes that aren't sex chromosomes e.g., chromosomes 1 to 22.

Balanced translocation

A translocation that involves a balanced exchange of chromosome material, with no net gains or losses of genetic material.


A biological property or substance(s) that is a sign of a normal or abnormal process, or of a condition or disease. A biomarker is used to determine how patients respond to treatments.


Early stage of an embryo, typically 5 days following fertilization. Consists of a cavity, an inner cell mass, and an outer trophectoderm.


Cell of embryo produced following fertilization and first cell division. Cells of the 8 cell stage embryo (typically day 3) are blastomeres.


A procedure that involves the sampling of cells or tissue for examination.


A cell is the functional unit of all known living things, it contains a complete set of chromosomes and all the molecules required for life.

Chorionic villus sampling (CVS)

A sampling of placental tissue (chorionic villus) that can subsequently be used for prenatal diagnostic testing. The sample is collected by putting a thin, flexible tube (catheter) through the vagina and cervix into the placenta or by inserting a long, thin needle put through the belly into the placenta.


An organized structure of DNA. There are 23 pairs in most cells of the human body (22 autosomal chromosomes, plus the sex-determining X and Y chromosomes). Chromosomes contain genes.

Chromosome screening

Another term for PGS; the procedure of screening chromosomes in embryos to ensure the correct number. Used with IVF.

Complete chromosome screening (CCS)

The procedure of screening all chromosomes in embryos to ensure the correct complement. Used with IVF.

Copy number imbalance

Any deviation from the normal chromosome numbers (2 copies of each).

Cystic fibrosis (CF)

The most common life-threatening autosomal recessive condition in the non-Hispanic white population, with an incidence rate of approximately 1 in 3,500 individuals in the United States. It affects the lungs most critically and also affects the pancreas, liver, and intestine. It is characterized by abnormal transport of chloride and sodium across an epithelium, leading to thick, viscous secretions.

Cystic fibrosis–related metabolic syndrome (CRMS)

A milder form of cystic fibrosis in which patients may present with manifestations of cystic fibrosis in only one or two organ systems (such as bilateral absence of the vas deferens or pancreatitis) and sweat chloride concentrations may not be clearly diagnostic. This milder form of cystic fibrosis has been termed “variant,” “atypical,” “nonclassic,” or “CFTR-related disease," and may present later in life.

Cystic fibrosis transmembrane conductance regulator (CFTR)

A protein that in humans is encoded by the CFTR gene. CFTR is an ABC transporter-class ion channel that transports chloride and thiocyanate ions across epithelial cell membranes. Mutations of the CFTR gene affect functioning of the chloride ion channels in these cell membranes, leading to cystic fibrosis and congenital absence of the vas deferens.


Clinical tests used to inform clinical decision making for the purpose of disease detection, screening, diagnosis, treatment selection, prognosis, and monitoring.


DNA, the acronym for deoxyribonucleic acid, is an informational molecule that encodes genetic instructions. DNA consists of a sequence of nucleotides commonly recorded as A, C, G, T. In cells, DNA usually exists as two long intertwined chains twisted into a double helix and joined by hydrogen bonds between the complementary bases adenine and thymine or cytosine and guanine. The chains are composed on nucleotides (a combination of any one of the nucleic acid sequence of nucleotides in DNA determines individual hereditary characteristics.

DNA Sequencing

The process of determining the precise order of nucleotides within a DNA molecule. It includes any method or technology that is used to determine the order of the four bases—adenine, guanine, cytosine, and thymine—in a strand of DNA. The advent of rapid DNA sequencing methods has greatly accelerated biological and medical research and discovery.

Egg screening

PGS or PGD procedures that are used during an IVF cycle to provide information about the egg or embryo so that only embryos with the correct number of chromosomes are selected for transfer, optimizing the chance of having successful pregnancy and a healthy baby.


Early developmental stage, from first cell division following fertilization to the 10th week of pregnancy, the following stage is a fetus.

Embryo screening

Procedures used to test embryos for abnormalities prior to implantation during IVF. A collective term for PGD and PGS.


The development process of the embryo.


Often used to describe an embryo with the normal number of 23 pairs of chromosomes, one of each pair inherited from the egg and sperm cell.


Fertilization is the fusion of an egg and sperm which eventually leads to the development of an embryo.


A stage of development during pregnancy that follows the embryonic stage (11th week of pregnancy) and continues to birth.


A sex cell, i.e., an egg or sperm that contains half the chromosomes of the parent. Gametes fuse during fertilization.


The process of forming gametes or sex cells, egg, and sperm. The process involves cell division known as meiosis.


A hereditary unit consisting of a sequence of DNA that occupies a specific location on a chromosome and determines a particular characteristic in an organism. Genes undergo mutation when their DNA sequence changes during cell division.

Genetic abnormality

Abnormality in genetic content of a cell. May include incorrect number of chromosomes (aneuploidy), structural imbalance, as well as genetic code changes.

Genetic code

The set of rules encoded using the bases of DNA (or mRNA) sequences. The nucleotide bases that form the DNA code are A, T, C, and G.

Genetic Test

A type of medical test that identifies changes in chromosomes, genes, or proteins. The results of genetic testing are used to confirm or rule out a suspected genetic condition or help determine a person's chance of developing or passing on a genetic disorder.


A human genome, or complete genetic code, consists of 22 pairs of chromosomes (autosomes) and a pair of sex chromosomes.

Immunoreactive trypsinogen (IRT)

A protein produced by the pancreas that is linked to cystic fibrosis. A blood test to determine IRT levels in newborns is part of the standard testing protocol for cystic fibrosis.


Implantation is the stage of pregnancy when the embryo adheres to the wall of the uterus. This occurs approximately 9 days after ovulation.

In vitro diagnostics (IVD)

In vitro diagnostic products are reagents, instruments, and systems that are used for diagnosing disease or other conditions, and include establishing the state of health, in order to cure, mitigate, treat, or prevent diseases. These products are intended for use in the collection, preparation, and examination of specimens taken from the human body.

In vitro fertilization (IVF)

In vitro fertilization (IVF) is a complex process that involves removing the eggs from a woman’s ovaries, fertilizing them with a man's sperm in a laboratory dish, and transferring the embryo to a woman’s uterus. A major treatment for infertility or fertility issues.

IVF cycle

A complex infertility treatment involving the removal of eggs from the woman, fertilization with a man’s sperm in a laboratory dish, and transfer of an embryo back into the woman’s uterus. Due to IVF failures and miscarriages, this procedure is often repeated so the prospective parents may undergo several “cycles.”


A comprehensive method for genome-wide linkage-based analysis of single-gene defects that can be used on an embryo in PGD.


An image of all the chromosomes from a cell as viewed through a microscope. Identifies the number and form of chromosomes.


The process of producing a karyotype. Performed by technicians who can identify chromosomes from their size and banding or staining pattern.


Process of cell division that produces two identical daughter cells, with the same chromosome complement as the parent cell.

Molecular Diagnostics

Diagnostic tests that identify a disease, predisposition for a disease, or progress in treating a disease by detecting specific molecules such as DNA, antibodies, and proteins.

Monogenic disorder

Genetic disorders caused by a mutation in a single gene. Examples include cystic fibrosis, Huntingdon's disease and sickle-cell anemia.


When there is one copy of a particular chromosome instead of the normal two.


Mutations are changes in a genomic sequence: the DNA sequence of a cell’s genome or the DNA or RNA sequence of a virus. Mutations are caused by radiation, viruses and mutagenic chemicals, as well as errors that occur during DNA replication. Mutation can result in several different types of change in DNA sequences. Change in genetic code can be benign or harmful and can include a wide range of changes from large-scale aneuploidy to single base changes, which can have either no effect, alter the product of a gene, or interfere with the gene’s functioning.

Newborn screening (NBS)

The practice of testing all babies for certain disorders and conditions that can hinder their normal development. Babies with these conditions appear healthy at birth but can develop serious medical problems later in infancy or childhood. Early detection and treatment can help prevent intellectual and physical disabilities and life-threatening illnesses.

Nucleic Acid

Any of various complex organic acids (e.g. DNA or RNA) that are composed of nucleotide chains.


Any of a class of organic compounds, including structural subunits of nucleic acids. Each consists of a molecule of a five-carbon sugar (ribose in RNA, deoxyribose in DNA) and a nitrogen-containing base, either a purine or a pyrimidine. The base uracil occurs in RNA, thymine in DNA, and adenine, guanine, and cytosine in both, as part of the nucleosides uridine, deoxythymidine, adenosine ordeoxyadenosine, guanosine or deoxyguanosine, and cytidine or deoxycytidine. Nucleosides usually have a phosphate group attached, forming nucleotides.

Oocyte (or egg)

The female germ cell that is involved in reproduction or egg cell. It contains half the normal number of chromosomes termed haploid.

Preimplantation genetics

Term that includes both PGS and PGD, screening eggs or embryos for genetic abnormalities prior to implantation in an IVF cycle.

Preimplantation genetic diagnosis (PGD or PIGD)

Screening embryos or oocytes for specific genetic disorders caused by a single gene defect, such as cystic fibrosis or myotonic dystrophy.

Preimplantation genetic profiling (PGP)

Similar to PGS - screening for detection of chromosome abnormalities such as aneuploidy, also includes translocations.

Preimplantation genetic screening (PGS)

Screening embryos for the correct number and type of chromosomes. PGS does not look for a specific genetic disorder.

Prenatal diagnosis

Testing for diseases in a fetus or embryo prior to birth. Intended to detect birth defects. Amniocentesis and ultrasound are often used.


The process during which two chromosomes exchange genetic information during meiosis.


The sibling, or other close relative of known disease status, used to identify the affected haplotype. A term relevant for Karyomapping.

Ribonucleic acid (RNA)

A chain of alternating phosphate and ribose units with the bases adenine, guanine, cytosine, and uracil bonded to the ribose. RNA molecules are usually single stranded and involved in protein synthesis.

Robertsonian translocation

A specific type of translocation when two chromosomes fuse near the middle or centromere. Only occurs with chromosomes 13, 14, 21, 22 and Y.


The technique used to map out the sequence of the nucleotides that comprise a strand of DNA.

Sex chromosomes

The chromosomes that determine sex. Men have an X and a Y chromosome, women have two X chromosomes.

Single embryo transfer (SET)

The technique of selecting only one embryo for transfer in an IVF cycle to lower the risk of multiple pregnancies.

Single gene disorder

Genetic disorders caused by a mutation in a single gene. Examples include cystic fibrosis, Huntingdon's disease and sickle-cell anemia.


The male germ cell that is involved in reproduction. It contains half the normal number of chromosomes termed haploid.

Structural imbalance

Defects in the structure of an individual chromosome that occur when there is too much or too little genetic material within the chromosome.

Sweat Test

The sweat test has been the “gold standard” for diagnosing cystic fibrosis (CF) for more than 50 years. When it is performed by trained technicians, and evaluated in an experienced, reliable laboratory, the sweat test is still the best test to diagnose CF. The sweat test can be completed on people of any age. However, some infants may not produce enough sweat to test.


A laboratory instrument used to amplify segments of DNA using PCR.

Translocation carrier

An individual who has a balanced translocation in their genome. Carriers typically show no physical symptoms until they try to have baby and then may experience difficulty in maintaining the pregnancy. When one parent is a translocation carrier there is a higher risk for miscarriage as the embryos may be formed with one of the chromosomes involved in the translocation.


A type of chromosome abnormality caused by rearrangement of parts of two or more different chromosomes.


When there are three copies of a particular chromosome instead of the normal two.

Unbalanced translocation

A translocation that involves an unbalanced exchange of chromosome material, with genetic information extra or missing.


An alteration in the normal sequence of a gene, the significance of which is often unclear until further study of the genotype and corresponding phenotype occurs in a sufficiently large population.


A quick freezing method used to preserve egg cells and embryos. The technique allows an egg taken in one cycle to be implanted in another.


Initial cell produced by fertilization when an egg and sperm first meet. The first stage of development.