Helpline: 0207 713 7486

Helpline: 0207 713 7486

Glossary of terms

Here is a glossary to help explain some of the more common terms 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 may be diagnosed in some babies. It is not a substitute for getting good information from your healthcare professionals. 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 means 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 but can be done later. A needle is passed through the mother's abdomen into the uterus, under ultrasound guidance, and a small sample of amniotic fluid surrounding the baby is taken. The fluid contains substances from the baby which can be tested for certain conditions 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 three weeks if the cells need to be grown for a full karyotype. For every 200 women who have this test at about 16 weeks it is likely that one will miscarry as a direct consequence of the test.
  • Amniotic Fluid - This is the fluid surrounding the baby which protects it during pregnancy and labour. It contains cells from the baby, which can be removed by amniocentesis and examined.
  • Anencephaly (anenkefally) - Anencephaly describes a condition when part of the baby’s skull and brain does not form properly. A major part of the baby’s skull is missing and this affects the brain development. Sadly, babies with anencephaly do not survive after birth. See also Neural Tube Defect.
  • Aplasia (a-playsia) - Total or partial failure of development of an organ or tissue.
  • Array CGH - Genomic microarray (Array CGH) is an advanced method of genetic testing of a sample from CVS or amnio. It can detect copy number changes in a baby's chromosomes. This means it looks for where there are deletions (bits missing) or duplications (where there are extra bits) in the baby's DNA that would not be identified through the full karyotype. It is now sometimes used instead of or as well as karyotyping.
  • Atresia (a-treesia) - 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 who carries an altered gene will show characteristics of the genetic disorder and has a 50% chance of passing it on to their 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 sonographers to help calculate a baby's gestation.


  • Cardiology - The science concerned with the structure, function and diseases of the heart. A cardiologist is a heart specialist.
  • 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. For example, 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 during the pregnancy.
  • Cephalic (kefallic) - Relating to the head.
  • Chorionic Villus Sampling (CVS) - This test, which is usually known as CVS or occasionally CVB (CV biopsy), is a prenatal test which can be performed early in pregnancy, from 11 weeks. A tiny sample of tissue from the edge of the placenta is taken by inserting a fine needle through the abdomen. The range of conditions that can be detected is similar to those for amniocentesis. For every 200 women who have this test one will miscarry.
  • Chromosome - A rod-like structure present in all the body's cells (apart from red blood cells) which stores the genetic information that determines how we develop. 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). The higher the number the smaller the size of the chromosome, so chromosome 1 is the largest.  Down's 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.
  • Cleft Lip and Palate – This is a developmental problem in babies when the upper lip or palate (roof of the mouth) is not joined properly. This means there is a gap in either the lip and/or palate. Very occasionally it can be related to a genetic syndrome.
  • Combined Screening Test - Between 11 and 13 weeks of pregnancy, a combination of the nuchal translucency measurement (see nuchal translucency below) and a blood sample from the mother. Two serum levels are taken from the blood sample:  pregnancy associated plasma protein-A (PAPP-A), and free beta human chorionic gonadotrophin (Free beta hCG). Together with the mother's age, these are used to estimate her chances of having a pregnancy with Down's, Patau's and Edwards syndrome. If the chance is higher than 1 in 150, a diagnostic test, such as CVS, will be offered.
  • Congenital Anomaly - An anomaly 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 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 have serious health implications.


  • 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 be terminated under general anaesthetic using this technique in which the cervix is dilated and the uterine contents are removed by implements and gentle suction.
  • Down’s syndrome - A chromosome abnormality in which there are three copies of chromosome 21 instead of two. It is also called Trisomy 21. The condition is characterised by distinctive facial features and varying degrees of learning difficulties and can be associated with heart and other health problems.
  • Deletion - Genetic material is missing on a chromosome.
  • Dilation – This is the medical term for enlarged or expanded.
  • Diaphragmatic Hernia (dya-framatic) - 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 enters the chest cavity and presses against the heart and lungs.
  • Dys - Used at the beginning of many words to mean difficult, abnormal or impaired, e.g. dysplasia.
  • Dysplasia (dis-playsia) - Abnormal development of skin, bone or other tissues.


  • Edwards' syndrome - A chromosome anomaly 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 medical term used when it is being done following a miscarriage or induced abortion. The placenta may be retained following a late termination and will need to be removed surgically.
  • Exomphalos – Also called omphalocele. This occurs when the abdomen fails to close around the base of the umbilical cord during the early development of the baby. This means some organs develop on the outside of the baby’s abdomen. This is usually the bowel but may include the liver and other organs. The sac containing the exposed organs is usually covered in a protective membrane.


  • 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 does not happen often.
  • 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 weeks 18-20 of pregnancy.
  • FL (femur length) - Measurement of thigh bone, used in ultrasound to help calculate a baby's gestation.


  • Gastroschisis (gastroskeesis) – This is a condition where the baby develops a hole in the abdominal wall during development. This is usually to the right side of the umbilical cord. Some of the bowel may slip through this hole and continue to develop outside the baby’s abdomen.
  • Gene - The unit of a chromosome through which particular characteristics are inherited.
  • Genetic Anomaly - A disorder arising from an anomaly in the chromosomes which may or may not be hereditary.
  • Genetic Counsellor - A healthcare professional who specialises in advising parents about inherited disorders and the likelihood of being 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.  A gynaecologist is the specialist in this area.


  • Haem- - Used at the beginning of words to mean blood, e.g. haemorrhage (bleeding) haemophilia (an 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.
  • Holoprosencephaly (HPE) (holoprosenkefally) - The front part of the baby’s brain fails to develop into clearly separate right and left halves. There are varying levels of severity.
  • Hydro- - This is used at the beginning of many words to mean water or watery fluid, e.g. hydrocephalus.
  • Hydrocephalus (hydrokefalus) - Hydrocephalus is due to an imbalance in the production and absorption of cerebrospinal fluid (CSF). This causes the ventricles in the brain to swell, putting pressure on the surrounding tissue. In babies this will make the head enlarge. It is sometimes called ‘water on the brain’.
  • 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 - a syringe used to inject a substance under the skin.
  • Hypoplasia (hypoplaysia) - Underdevelopment of an organ or tissue.


  • Inherited - Having a hereditary characteristic passed down through a family; 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 a screening test for Down’s syndrome 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 concentrations of serum pregnancy associated plasma protein-A (PAPP-A) and free beta human chorionic gonadotrophin (freeß-hCG). A nuchal translucency scan is also carried out. The second stage involves a second blood sample which is ideally taken at 15 or 16 weeks of pregnancy. This blood sample measures four serum levels - alpha feto protein (AFP), unconjugated oestriol (uE3), free beta human chorionic gonadotrophin (freeß-hCG) (or sometimes total 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. Only after this second stage is a statistical result given. Women with a chance greater than 1 in 150 are offered amniocentesis.
  • IUGR (intrauterine growth restriction) - A condition which leads to a baby being born extremely small for its gestational dates.


  • Karyotype (carriotype) - 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. This allows major chromosomal changes to be detected. It is labour-intensive and the report from the laboratory can take up to three weeks.


  • MRI (Magnetic Resonance Imaging) - A way of analysing body tissues by using radio waves and a magnetic field. It is particularly useful for examining the brain, central nervous system and musculoskeletal system. It is a non-invasive diagnostic tool and it can be used in pregnancy as it does not use potentially harmful radiation as in x-rays. It is usually done later in pregnancy, after the 18-20 week anomaly scan.
  • 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 anomaly 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. A neonatologist is the specialist in this area.
  • Neural Tube - The structure in an embryo from which the brain and spinal cord form.
  • Neural Tube Defect (NTD) - There are several types of neural tube defect including spina bifida. An NTD is an anomaly where the spine has not closed over the central nervous tissue. This hole is known as a lesion. If this 'lesion' is at the head, the skull bones do not develop properly. The condition is called anencephaly and means the baby will not survive after birth. 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. 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.
  • Non-invasive prenatal testing (NIPT) – This kind of testing uses a maternal blood test to analyse cell free fetal DNA present in the mother’s blood. It can give an accurate assessment of the baby’s chance of having Down’s syndrome. It can also be used for fetal sexing and to detect some single gene disorders.
  • Nuchal Translucency Scan - Between 11 and 13 weeks of pregnancy the fluid at the back of the baby's neck, the nuchal translucency, is measured. By combining a blood test and 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 150 (although this may vary with different hospitals) a diagnostic test, such as CVS, will be offered. This is the only screening test that can be offered in twin pregnancies.
  • Neurology - The branch of science that deals with the structure, functioning and diseases of the nervous system.


  • Oligohydramnios - A condition in which there is too little amniotic fluid. This can affect the baby’s growth.


  • Paediatrics – The branch of medicine concerned with child health. A paediatrician is the specialist in this area.
  • Patau’s syndrome - A chromosome anomaly 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 will usually have very short lives and require specialised nursing. Some babies can be cared for at home and may live longer than first predicted but with very severe disabilities.
  • -plasia (playsia) – Used at the end of a word to mean formation or development e.g dysplasia.
  • Poly- Used at the beginning of a word to mean many e.g polycystic.
  • Polyhydramnios – A condition in which there is too much amniotic fluid. It can lead to premature delivery and sometimes indicates other anomalies.
  • Postpartum – Concerning the first days after birth.
  • Pulmonary - To do with the lungs.


  • Quadruple (quad) Test - This is a screening test for Down’s syndrome that is usually offered to women who were unable to have combined screening. 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 following substances will be taken from the blood sample and measured: alpha-fetoprotein (AFP), inhibin-A, unconjugated oestriol (uE3) and free beta human chorionic gonadotrophin (free ß-hCG) or total 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. Women with a statistical chance greater than 1 in 150 are offered amniocentesis. This test does not screen for Patau's or Edwards syndrome.


  • Rapid Testing for Down’s Syndrome - FISH (fluorescent in situ hybridisation) and QF-PCR (quantitative fluorescentpolymerase chain reaction) are laboratory techniques that can provide results quickly after a CVS or amniocentesis.  Both are methods of analysing DNA extracted from samples taken. Down’s, Edwards' and Patau’s syndromes can be identified and the results made available within 72 hours.  Not all the chromosomes are checked; this is done during a full karyotype of cells from the amniotic fluid or CVS and it can take two to three weeks to obtain the results from this.
  • Renal – To do with the kidneys.


  • 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.
  • Soft Markers – This is an obsolete term. Now the phrase 'normal variant' is preferred. They are slight variations from the normal anatomy seen at the 18 – 21 week scan or sometimes slightly earlier, which may or may not indicate a problem. In themselves, they are not harmful to the baby; most have no significance whatsoever and usually disappear in a matter of weeks. The reason they are reported is that very occasionally, they may be a sign of an underlying chromosomal anomaly.
  • Spina Bifida - See Neural Tube Defect.
  • Syndrome – A group of symptoms which regularly occur together, or a condition which is characterised by a set of associated symptoms.


  • Translocation – Happens when there is a rearrangement in which a part of one chromosome is transferred to another with a different number.
  • 3D/4D Scans – There are scanning machines that use computer imaging to create a three dimensional picture of the baby in the womb. 4D simply means that you can see the baby in real time. These scans can provide clear and often memorable images of the external structures and features of the baby but are no better than conventional ultrasound at detecting anomalies. They are not offered as standard on the NHS.
  • Triploidy – The presence of a full extra set of chromosomes. Sadly babies with this condition do not usually survive after birth.
  • Trisomy - Where there are three chromosomes rather than the usual pair. For example, Down’s syndrome is also called Trisomy 21 because there are three copies of chromosome 21 instead of two.


  • 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 fetal anomalies). Detailed scanning at 18 to 21 weeks checks for a range of fetal anomalies.


  • Ventricle (heart) - Either of the two lower chambers of the heart which both have thick muscular walls. The left ventricle is thicker than the right.
  • Ventricle (brain) – One of the four cavities in the brain which are filled with fluid.

ARC's national helpline

Want to talk? We’re here as often as you need us. Our helpline is answered by trained staff Monday to Friday, 10.00am-5.30pm; call 0207 713 7486.