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Glossary of terms

Here is a glossary to help explain some of the more common terms that you may come across. It does not cover the more complicated terminology associated with genetics and does not include details about the rare disorders that will be diagnosed in some babies. It is not meant to be a substitute for getting good information from those professionals responsible for looking after you. If they use words and language that you do not understand, feel able to ask them to repeat what they have told you and to explain themselves more clearly.

A(n) - used at the beginning of many words to mean that something is missing, lacking or it can simply mean not, e.g. acardia (absence of the heart), amorphic (lacking definite shape) atypical (not usual)

AC (abdominal circumference) - measurement used in ultrasound to help calculate a baby's gestation.

Agenesis (a-genesis) - in medical terms, agenesis means absence of something. Agenesis of the corpus callosum In this case, a part of the brain that joins the two hemispheres together is missing. Renal agenesis means the kidneys are missing.

Amniocentesis - This test is usually done around the 16th week of pregnancy. A needle is passed through the mother's abdomen into the uterus, under ultrasound guidance, and a sample of amniotic fluid surrounding the baby is withdrawn. The fluid contains substances from the baby which can be tested for certain conditions such as neural tube defects - spina bifida and anencephaly - and cells which can be grown in culture. The cells can be tested for Down's syndrome and other chromosomal and inherited disorders. Results will take about a week if the tests are on the fluid and up to 4 weeks if the cells need to be grown for chromosome analysis. For every 100-200 women who have this test at about 16 weeks it is likely that one will miscarry as a direct consequence of the test.

AMNIO Q-PCR and AMNIO + F.I.S.H. - Following the normal procedure for amniocentesis, fluid is taken from the amniotic sac surrounding the baby under ultrasound guidance. The fluid contains cells from the baby. Amnio-PCR and Amnio + F.I.S.H. are molecular tests which provide a rapid diagnosis of the three most common chromosome abnormalities including Down's syndrome. Results take on average 2 to 7 days. At the moment only a few hospitals offer this to women. However many hospitals do have access to the facilities for performing these tests and often the tests can be paid for on a private basis.

Amniotic Fluid - This is the fluid surrounding the fetus in the uterus which protects it during pregnancy and labour. It contains substances and cells from the baby, which can be removed by amniocentesis and examined.

Anencephaly - See Neural Tube Defect.

Anomaly - A malformation or abnormality in any part of the body.

Aplasia - total or partial failure of development of an organ or tissue.

Atresia (atreesia) - absence or abnormal narrowing of a body opening, e.g. duodenal atresia, the narrowing of part of the small intestine that consequently causes an obstruction.

Autosome - any chromosome that is not a sex chromosome.

Autosomal Dominant - describes a situation in which the person possessing an altered gene will show characteristics of the genetic disorder and has a 50% chance of passing it on to a child.

Autosomal Recessive - describes a situation in which the carrier of an altered gene does not show any characteristics of the disorder. The baby of two carriers of the altered gene has a 25% chance of inheriting the disorder.

BPD (biparietal diameter) - measurement of two bones in the skull used by ultrasonographers to help calculate a baby's gestation.

Cardiology - the science concerned with the structure, function and diseases of the heart. cardiologist

Centile Chart - chart used to assess a baby's/child's physical development. The lines of growth on the chart are called centiles. The number of the centile (from one to a hundred) predicts the percentage of babies/children who are below that measurement for a particular age. E.g. if a baby falls within the 10th centile, it means 10% of all babies will be smaller and 90% will be bigger. A baby would be expected to stay within the same centile.

Cephalic (kefallic) - relating to the head.

Chorionic Villus Test - This test, which is usually known as CVS (CV sampling) or CVB (CV biopsy), is a prenatal test which can be performed early in pregnancy, from 11 weeks. A sample of tissue that will form the placenta is taken either through the cervix or through the abdomen. The range of conditions that can be detected is similar to those for amniocentesis except that neural tube defects cannot be diagnosed. For every 100 women who have this test from the 11th week in pregnancy one will miscarry.

Chromosome - a rod like structure present in all the body's cells (apart from red blood cells) which stores genetic information. Normally, humans have 23 pairs. The sperm and ova contain 23 each which combine at fertilization to create 46. Each chromosome pair is given a number to describe it, from 1 to 23 (number 23 is the pair of sex chromosomes, XX or XY). e.g. Down syndrome describes a condition in which the baby has three of chromosome 21 rather than the usual pair, so it is also known as Trisomy 21.

Chromosome Abnormality - A change in the number or arrangement of the normal 23 pairs of chromosomes.

Combined Test - Between 11 and 13 weeks of pregnancy, a combination of the nuchal scan measurement (see Nuchal Scan below) and a blood sample from the mother which measures the concentration of two serums: pregnancy associated plasma protein-A (PAPP-A), and free beta human chorionic gonadotrophin (Free beta hCG); together with the mother's age, are used to estimate her chances of having a pregnancy with Down's syndrome. If the chance is more than 1 in 250 (although this does vary with different hospitals) a diagnostic test, such as CVS, will be offered.

Congential Abnormality - An abnormality present at birth, although not necessarily hereditary.

consultant - a highly trained specialist in a branch of medicine who accepts total responsibility for patient care.

CRL (crown rump length) - measurement of baby from top of the baby's head to its bottom used in ultrasound to help calculate gestation.

Cyst - an abnormal sac or closed hole containing liquid or semi-solid matter. cystic

Cystic hygroma - cyst on lymphatic vessels, usually around the head and neck region. These cysts can vary enormously in size, from a small growth on the neck to a very large mass of growths which can seriously inhibit eating.

D & C (Dilatation and Curettage) - A procedure in which the cervix is gently opened and a loop shaped instrument is inserted to scrape away the inner lining of the uterus.

D & E (Dilatation and Evacuation) - Pregnancies can sometimes be terminated under general anaesthetic using this technique in which the cervix is dilated and the uterine contents are removed by suction.

Downs Syndrome - A chromosome abnormality in which there are 3 copies of chromosome 21 instead of 2. It is also called Trisomy 21. The condition is characterised by distinctive facial features and varying degrees of learning difficulties and is often associated with lung and heart problems.

Deletion - genetic material is missing on a chromosome.

Diaphragmatic Hernia (dyafrematic) - sometimes referred to as a congenital diaphragmatic hernia (CDH) a hole in the diaphragm which the bowel can pass through. This could affect the development of a baby's lungs if the bowel goes up into the chest and then squashes against the heart and lungs.

Dys- - used at the beginning of many words to mean difficult, abnormal or impaired, e.g. dysplasia

Dysplasia (displaysia) - abnormal development of skin, bone or other tissues.

Edwards Syndrome - A chromosome abnormality in which there are three copies of chromosome 18 instead of two. It is also called Trisomy 18. The condition means that the baby may not survive pregnancy, or may have a short life and require specialised nursing, but some babies can be cared for at home and may live longer than first predicted.

ERPC - Evacuation of the Retained Products of Conception. The procedure is as described above for D & C, but ERPC is the technically correct phrase when it is being done following a spontaneous or induced abortion. The placenta may be retained following a late termination and needs to be removed surgically. The phrase is felt by many women to be rather callous.

False Negative - Some women are told that tests have shown that their baby does not have a particular problem, only to find out when the baby is born that this is not true. This is called a false negative result and is not a common occurrence.

False Positive - Some women are told that tests have shown that their baby may have a problem. If further tests then show that this is not the case, that result is called a false positive.

Fetoscopy - a special fibre optic instrument is passed through the abdomen of a pregnant woman to examine the baby. If required, it is usually done in the 18th-20th week of pregnancy.

FL (femur length) - measurement of thigh bone used in ultrasound to help calculate a baby's gestation.

Gene - The unit of a chromosome through which particular characteristics are inherited from one or both parents.

Genetic Abnormality - A disorder arising from an abnormality in the chromosomes which may or may not be hereditary.

Genetic Counsellor - a health professional who specialises in advising parents about inherited disorders and the likelihood of becoming affected or having affected children. He or she can also give information on what may be available in order to prevent, diagnose and manage such conditions.

Gynaecology - the study of diseases of women and girls, particularly those affecting the female reproductive system. Gynaecologist

Haem- - used at the beginning of words to mean blood, e.g. haemorrhage (bleeding) haemophilia (inherited disorder in which blood clots very slowly).

Hereditary - describes how characteristics are transmitted through families within the chromosomes of the fertilising egg and sperm.

Hydro- - This is used at the beginning of many words to mean water or watery fluid, e.g. hydrocephalus.

Hydrocephalus - Hydrocephalus is due to an imbalance in the production and absorption of cerebrospinal fluid (CSF). This causes the ventricles in the brain to swell, causing pressure on the surrounding tissue. The causes vary, but it is rarely genetic. The effects of hydrocephalus vary significantly, but the outlook for those where it is detected in the womb is generally very poor.

Hydrops - an abnormal build-up of fluid in body tissues or cavities hydrops fetalis describes severe swelling that develops before birth most often because of anaemia.

Hyp(o)- - This is used at the beginning of many words to mean deficiency, lack or small size, e.g. hypoplasia. When speaking anatomically it can also mean under, e.g. hypodermic needle - syringe used to inject a substance under the skin.

Hypoplasia (hypoplaysia) - underdevelopment of an organ or tissue.

Inherited - Having a hereditary characteristic; this can be eye colour, a personality type or a disease.

Intra- - used at the beginning of words to mean inside or within, e.g. intrauterine - within the uterus.

Integrated Test - The integrated test is performed in two stages. In the first stage, at around 12 weeks of pregnancy, a blood sample is taken from the mother which measures the concentration of serum pregnancy associated plasma protein-A (PAPP-A) and a nuchal scan is also carried out. The second stage involves a second blood sample which is ideally taken at 15 or 16 weeks of pregnancy. Only after this second stage is a statistical result given. This blood sample measures four serum levels - alpha feto protein (AFP), unconjugated oestriol (uE3), free beta human chorionic gonadotrophin (freeß-hCG) and inhibin-A (inhibin). The measurement of the total six markers together with the mother's age are used to estimate her chances of having a pregnancy with Down's syndrome. Women with a chance greater than 1 in 100 are offered amniocentesis.

IUGR (intrauterine growth retardation) - a condition which leads to a baby being born extremely small for its gestational dates.

Karyotype - this is done after an invasive test. In the laboratory all the baby's chromosomes are carefully analysed under a microscope and organised in numbered order. They will be able to detect chromosomal disorders by doing this.

Magnetic Resonance Imaging (MRI) - a way of analysing body tissues by using radio waves and a magnetic field. It is particularly useful for examining the central nervous system and musculoskeletal system. It is a non-invasive diagnostic tool and it does not use potentially harmful radiation as in x-rays.

Microcephaly (microkefali) - a condition in which the brain is not fully developed and the head is very small in relation to the rest of the body.

Monosomy - the absence of one of a pair of chromosomes.

Mosaicism - where a genetic or chromosomal abnormality occurs in some body cells. The proportion of normal to abnormal cells will determine how serious the condition is.

Neonate - used to refer to a baby in the first four weeks of life. Neonatal, neonatologist

Neural Tube - the structure in an embryo from which the brain and spinal cord form. neural tube defects (NTDs) occur when this does not form properly. There are several types of NTD, including spina bifida.

Neural Tube Defect (NTD) - An abnormality where the spine has not closed over the central nervous tissue. If this 'lesion' is at the head, the condition is called anencephaly and is incompatible with life. If it occurs anywhere lower down the spine it is called spina bifida and results in varying degrees of physical and mental disability. Detailed ultrasound scanning is the way in which these abnormalities are confirmed, often following a raised AFP blood test. Most NTDs are 'open' which means that there is no skin over the lesion in the spine; about 1 in 7 cases of spina bifida are 'closed' which means that although the spine has not covered the nervous tissue there is a covering of skin. These closed conditions are less likely to be detected antenatally by the AFP test.

Nuchal Scan - Between 11 - 13 weeks of pregnancy the fluid at the back of the baby's neck, the nuchal translucency, is measured. By combining the mother's age with information from the scan an individual statistical chance of a chromosome abnormality can be given for that particular pregnancy. If the chance is more than 1 in 250 (although this does vary with different hospitals) a diagnostic test, such as CVS, will be offered.

Neurology - the branch of science that deals with the structure, functioning and diseases of the nervous system. neurologist

PATAU'S SYNDROME - A chromosome abnormality in which there are three copies of chromosome 13 instead of two. It is also called Trisomy 13. Babies with a full trisomy 13 may not survive pregnancy, or may have short lives and require specialised nursing, but some can be cared for at home and may live longer than first predicted.

SCANS - See Ultrasound scanning.

SEX CHROMOSOMES - The 23rd pair of chromosomes are the sex chromosomes. There are two sorts, an X and a Y. Females have two X chromosomes (XX) and males have one X and one Y chromosome (XY). Sometimes babies are found to have an extra sex chromosome or one missing. The effect of this on the mental and physical condition of the baby is very hard to predict. It is very important to receive Genetic Counselling in order to receive accurate and up to date information.

SPINA BIFIDA - See Neural Tube Defect.

SYNDROME - Combination of symptoms and signs grouped together to form a disorder.

TRIPLE TEST - This test has many names - you may hear it called the Leed's test, the Bart's test, the double test or the blood test. A sample of blood is taken usually between 16-18 weeks of pregnancy. The stage of pregnancy is best estimated by an ultrasound dating scan. The number of substances measured will vary according to hospital policy but they will be a combination of alpha-fetoprotein (AFP), unconjugated oestriol (uE3) inhibin-A (inhibin) and free beta human chorionic gonadotrophin (free ß-hCG). The concentrations of these substances are used together with the mother's age to estimate her chances of having a pregnancy with Down's syndrome. The level of AFP is also used to determine if there is an increased chance of spina bifida or anencephaly. Women with a statistical chance greater than 1 in 250 (although the figure does vary at different hospitals) are offered amniocentesis. One in every 20 women will be given a chance higher than 1 in 250.

TRISOMY - Where there are three chromosomes rather than the usual pair, this is called a trisomy

ULTRASOUND SCANNING - This is a technique used routinely in most hospitals to monitor the growth and development of the baby before birth. Scans before 16 weeks are useful for dating the pregnancy (and are able to detect some major malformations), detailed scanning at 18-21 weeks should show up any major malformations as well as some minor ones.