FAQs - Section 10: Glossary

A medical procedure in which the obstetrician inserts a fine needle into the uterus and collects a sample of the amniotic fluid which surrounds the developing baby. Cells in the amniotic fluid come from the fetus, not from the placenta, and provide the most accurate indication of the genetic status of the fetus.

A term which describes the presence of an abnormal number of chromosomes.

A medical procedure in which the obstetrician inserts a fine needle into the uterus and collects a sample of the placenta. Cells in the placenta come from the same fertilised egg as the fetus and provide a good indication of the genetic status of the fetus.

A bundle of DNA, i.e. the genetic code, inside a cell. The DNA of a human cell is present as 46 pairs of chromosomes which can be examined by a microscope.

A chromosome disorder due to a microdeletion on chromosome 22. The precise location is called 22q11.2, and 20–30 genes are typically missing from the chromosome.

A chromosome disorder due to deletion 22q11.2.

Twins that developed from two fertilised eggs.

A chromosome disorder due to the presence of a third copy of chromosome 21.

A chromosome disorder due to the presence of a third copy of chromosome 18.

A term which describes the presence of the normal number of chromosomes.

A term which describes a normal test result which is incorrect.

A term which describes an abnormal test result which is incorrect.

The proportion of DNA fragments in the mother’s blood which have come from the fetus or placenta.

Measurement of the concentration of selected biochemical markers in maternal blood at 12–14 weeks’ gestation. The pattern of concentrations, together with certain ultrasound measurements, give an indication of the probability that the fetus has a chromosome disorder.

A term to describe low levels of calcium in the blood. This can cause fits and other medical problems if it is not corrected.

A term to describe amniocentesis and CVS, both of which require a needle being placed close to the developing baby to obtain a sample of fluid or tissue.

A mild chromosome disorder in which a male has an additional Y chromosome.

A term to describe the result of detailed microscopic examination of the number and structure of chromosomes in cells.

A chromosome disorder in which a male has an additional X chromosome.

A term to describe any abnormality of structure of the developing baby or child.

The loss of a small portion of a chromosome that is too small to be detectable by microscopic examination of chromosomes.

A chromosome abnormality in which a numbered chromosome, e.g. 21, 18 or 13, is missing.

Twins that have developed from a single fertilised egg.

An abbreviation for a non-invasive prenatal test. This type of testing is sometimes called non-invasive prenatal screening. These tests involve the analysis of DNA fragments in the maternal blood, and do not require that a needle be positioned close to the developing baby.

The probability that a normal test result is correct.

A chromosome disorder due to the presence of a third copy of chromosome 13.

The probability that an abnormal test result is correct.

The accuracy of a test in correctly identifying samples known to be normal.

A mild chromosome disorder in which a female has a third X chromosome.

A chromosome disorder in which there is a third copy of chromosome 13.

A chromosome disorder in which there is a third copy of chromosome 18.

A chromosome disorder in which there is a third copy of chromosome 21.

A term which describes a normal test result which is correct.

A term which describes an abnormal test result which is correct.

A chromosome disorder in which a female has only one X chromosome.

A chromosome disorder due to 22q11.2 deletion.