Your guide to health and prenatal genetics
Mother hold baby

Assess your personalised prenatal risks, choose screening tests, and find nearby maternity clinics

Knowledge hub


microdeletion syndrome, characterized by many clinical problems, including cardiac defects, hypoparathyroidism, T-cell immunodeficiency, and facial dysmorphism. Also called Di George syndrome, type II.
a microdeletion disorder characterised by developmental delay, brain abnormalities, heart defects, hearing loss, severe intellectual disorder and behavioural problems. Prevalence 1 in 5,000-10,000.
Describes the proportion of all tests that really give correct results. For rare conditions, as is often the case for conditions screened with NIPT/cfDNA, the majority of individuals screened will be correctly identified as “negative” and therefore NIPT/cfDNA is described as “highly accurate”. However, the chance that any positive result is a true positive result depends on the Positive Predictive Value (PPV) of the test (see PPV). It is important to note that although the prior probability of many chromosome conditions is influenced by maternal age, other factors such as maternal serum biochemical screening (MSS) results and ultrasound markers (e.g. NT scan) may also indicate the higher likelihood of a condition in an individual pregnancy.
an abnormal number (extra or missing) of chromosomes in a cell which usually results in chromosomal disorder.
short DNA fragments that naturally circulate freely in the bloodstream.
is an invasive prenatal test which can be performed early in the pregnancy from 11 to 13 weeks. A tiny sample of tissue from the edge of the placenta (chorinic villi) is taken by inserting a fine needle guided by ultrasound through the abdomen or the cervix, from whom extracted DNA is analysed in molecular laboratory to detect chromosomal diseases. There is around 1 in 200-300 risk of miscariage for CVS.
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 male sperm and female 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).
a microdeletion syndrome, chracterised by intellectual disability, developmental delay, small head size (microcephaly), hypotonia, distinctive faces, heart defects and a characteristic cat-like cry. Prevalence 1 in 20,000-50,000.
the most common microdeletion syndrome characterised by characteristic head and face anomalies, cleft palate, mental retardation, immunodeficiency due to absent thymic gland, low calcium in blood and certain heart defects. Prevalence 1 in 2,000-4,000. Also called velocardiofacial, CATCH-22 syndrome.
or Trisomy 18 (T18) - a chromosome anomaly (aneuploidy) in which there are three copies of chromosome 18 instead of two and is associated with a high rate of miscarriage. Infants born with trisomy 18 often have congenital heart defects as well as various other medical conditions, shortening their lifespan and unfortunately die within the first few weeks of life while less than 10% live beyond one year. Prevalence of T18 is approximately 1 out of every 5,000 newborns
A situation, when tests results have shown that a baby does not have a particular problem, but it was however found out later on after birth. This is called a false negative result and does not happen often.
Relating to the unborn baby.
The amount of the cell-free DNA (cfDNA) in the maternal blood that is of fetal origin which is on the average about 10% at 16 week of gestation; it typically increases later in the pregnancy and is essential for accurate test results.
The most frequently used estimate of the age of the pregnancy, calculated from the start of mother’s last menstrual period (LMP), which is ussualy two weeks (or 14 days) before the baby was conceived (see “fetal age”). Pregnancy is calculated from this day because each time a woman has a period, her body is preparing for pregnancy. Gestational Age = Fetal Age + 2 weeks.
a microdeletion syndrome, characterized by developmental delay, cognitive impairment, distinctive faces, bleeding disorders and some behaviour disorders. Prevalence 1 in 100,000.
a microdeletion syndrome, characterized by benign bone tumours (exostoses), short stature, intellectual disability and distinctive facial features. Also called trichorhinophalangeal syndrome type II.
or Turner syndrome – sex chromosomes aneuploidy, which is caused by a completely or partially missing X sex chromosome in females (X0). Females with Turner syndrome have a wide range of symptoms and some distinctive characteristics, like short stature, underdeveloped ovaries, lack of monthly periods, infertility and learning difficulties. Occurs in about 1 in 2,500 of all newborn girls.
Represents the proportion of negative test results that are truly negative. NPV answers your question: “If my NIPT result is negative, what is the chance that my baby is really unaffected?” For example, if the NPV is 99%, then approximately 99% of individuals who have that negative test result would be expected to have an unaffected pregnancy. In this example, 1% of women receiving a negative result will have an affected pregnancy (false negative result). As PPV, NPV slo depends on the prevalence of the condition being tested for – the rearer is the condition (e.g. microdeletion), the more higher is NPV (e.g. the negative result gives more peace of mind).
Non-Invasive Prenatal Test – refers to the accurate modern molecular genetic screening of maternal and fetal cell-free DNA from a pregnant women’s blood to assess the risk for an unborn baby to have fetal chromosomal anomalies (e.g. aneuploidies, microdeletions), avoiding the risk of miscarriage inherent for invasive diagnostics methods, such as amniocentesis or CVS. It can also be used for fetal sexing and to detect some single gene disorders.
or Trisomy 13 (T13) – a chromosome anomaly (aneuploidy) in which there are three copies of chromosome 13 instead of two and is associated with a high rate of miscarriage. Infants born with trisomy 13 usually have severe congenital heart defects and other medical conditions. Survival beyond the first year is rare, most babies will not survive beyond the first weeks of life. Prevalence of T13 is approximately 1 out of every 16,000 newborns.
is a neurodevelopmental disorder, due to microdeletion of the imprinted region 15q11 on paternally inherited chromosome 15. PWS a clinically distinct from Angelman syndrome, and results in hypotonia, extreeme obesity, behavioural problems and infertility. Prevalence 1 in 10,000-20,000. Also see "Angelman syndrome".
A pregnancy with a single baby
One third of a normal pregnancy. First trimester (0 to 13 weeks), seceond trimester (14 to 26 weeks), Third trimester (27-40 weeks).
a chromosome abnormality (aneuploidy), when a baby has three copies of chromosome 16, instead of two. Full trisomy 16 is incompatible with life and unfortunately most women will miscarry in the first trimester.
a chromosome abnormality (aneuploidy), when a baby has three copies of chromosome 9, instead of two. Babies born with trisomy 9 commonly have defects in the heart, kidneys, and musculoskeletal system.
a microdeletion syndrome, chracterised by a distinctive facial appearance (Greek warrior helmet), developmental delay, intellectual disability, and seizures. Prevalence 1 in 50,000.
or 48, XXYY - a sex chromosome aneuploidy, which due to extra XY chromosomes causes medical and behavioral problems in males, which are similar to Klinefelter (XXY) syndrome, but more severe. It affects 1 in 18,000 to 50,000 males.
microdeletion of this region causes developmental delay, cognitive impairment (from mild to profound), dysmorphic facies, growth impairment, hearing loss, cardiac malformations, epilepsy, and psychiatric and behavioral problems.
a microdeletion syndrome, characterized by intellectual disability of variable severity and dysmorphic facial features, microcephaly (small scull), cleft palate, seizures and behavioural problems. Also called GLASS syndrome.
Amniocentesis – An invasive prenatal diagnostic test, which is usually done around the 16th week of pregnancy (from 15 to 22 week). Under ultrasound guidance a needle is passed through the mother's abdomen into the uterus and a small sample of amniotic fluid surrounding the baby is taken. The amniotic fluid contains substances from the baby which can be tested for certain genetical conditions and fetal cells which can be grown in culture. The fetal 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 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 (0,5-1%), although recent studies show much smaller miscariage risk (1/300-400).
or “happy-puppet syndrome” is a neurodevelopmental disorder, due to microdeletion of the imprinted region 15q11 on maternally inherited chromosome 15. AS is characterized by mental disability, movement or balance disorders, and severe limitations in speech and language. Prevalence 1 in 10,000-20,000. Also see "Prader-Willi syndrome".
an admixture of DNA fragments from fetus present in maternal blood serum during pregnancy. On average maternal cfDNA constitutes 90% and cffDNA – around 10%.
A change in the number or arrangement of the normal 23 pairs of chromosomes.
an anomaly present at birth, although not necessarily hereditary.
Refers to missing genetic material (microdeletion) on a chromosome or DNA.
or Trisomy 21 (T21) - a chromosome abnormality (aneuploidy) which results in three copies of chromosome 21 instead of two. This disease is characterised by distinctive facial features, mental impairment, varying degrees of learning difficulties, heart and other health problems. Children born with Down Syndrome will need extra medical care depending on the child’s specific health problems. Prevalence of T21 is 1 out of every 700 newborns.
A method used in reproductive medicine in which an egg is harvested from a woman, fertilised outside of the body, and then implanted into a recipient woman who will carry the pregnancy.
A situation, when initial tests results have shown that a baby may have a helath problem, but furhter tests did not confirm that.
or Embryonic age - the actual age of the baby starting at the time of conception. Fetal Age = Gestational Age – 2 weeks.
Is a combination of specific prenatal tests – ultrasound (measuring nuchal translucency) and a biochemical maternal blood serum screening of PAPP-A (Pregnancy-associated plasma protein A) and free β-hCG (ß-chain of the human chorionic gonadotropin). Typically, first trimester screening (or so called combined screening) is done between weeks 11 and 14 of a pregnancy to determine the likelihood of fetal chromosomal disroders (e.g. trisomy 21, 18 or 13).
Is a method of assisted insemination when the actual fertilisation takes place outside of the body and artificially fertilised egg is then implanted back into a woman’s womb for a normal pregnancy.
Chromosomal disorder that affects only males and is characterised by an extra X-chromosome in all, or in a proportion, of the cells of the body. Males with Klinefelter’s syndrome have underdeveloped testes low male hormone testosterone, which results in infertility, increased breasts (gynecomastia), behaviouraland learnign problems. It affects 1 in 500 to 1,000 newborn males.
Molecullar technology that can use very small amounts of starting material (DNA or RNA) to analyse expression or variation of thousands of genes simultaneously.
see NGS (Next generation sequencing)
Refers to the high-throughput sequencing (i.e. reading) of prepared DNA or RNA samples using recent genomic technologies, what allows to perform sequencing much more quickly and cheaply than the previously using older sequencing methods, and as such have revolutionised the study of molecular biology and genomics, including non-invasive prenatal diagnostics.
An ultrasound measurement for the accumulation of fluid in the under the skin at the neck area of the unborn child as part of first-trimester screening. A higher nuchal translucency may indicate the presence of chromosomal or other disorders of the unborn child.
or Test precision - represents the proportion of positive test results that are truly positive. PPV answers your question: “If my NIPT result is positive, what is the chance my baby is really affected?” For example, a PPV of 25% indicates that only quarter of the cases who have a positive test result are predicted to be actually affected with the disease. The PPV is dependent on the prevalence of the disease. The rarer the condition, the lower the PPV (when sensitivity and specificity remain unchanged). Higher prevalence increases positive predictive value.
Also called the detection rate or true positive rate – measures the proportion of all individuals with a condition (i.e. “positives”) who are correctly identified as “positive” by a screening test (i.e. “true positives”). If 1,000 tested individuals have a given condition and 990 of them test “positive“ for that condition, the test’s sensitivity is 99%. Sensitivity = “true positives”/”positives” = “probability of a positive test given that the patient has the disease” = 990/1,000 = 99%; higher sensitivity means more sick people are identified as sick and not missed.
or True Positive Rate - measures the proportion of all individuals without a condition (i.e. “negatives”) who are correctly identified as “negative” by a screening test (i.e. “true negetives”). If 99,000 out of 100,000 unaffected individuals do not have a condition and 98,000 test “negative”, the test’s specificity is 99%. Specificity = “true negatives”/”negatives” = “probability of a negative test given that the patient is healhy” = 98,000/99,000 = 99%; higher specificity means less healthy people are incorrectly identiefied as sick.
A trisomy (an aneuploidy) is a chromosomal condition that occurs when there are three copies of a particular chromosome instead of the expected two. The risk of having a baby with a trisomy increases with maternal age. Most common trisomies are related to 21, 18 and 13 chromosomes.
a chromosome abnormality (aneuploidy), when a baby has three copies of chromosome 22, instead of two. Trisomy 22 is very rare. Unfortunately, pregnancies diagnosed with trisomy 22 are at very high risk of miscarriage or stillbirth.
microdeletion of this region (IRF6 gene) can result in syndorme, which is characterised by cleft lip and/or palate, increased risk of delayed language development, learning disabilities, or other mild cognitive problems.
a sex chromosome aneuploidy, which is characterized by the presence of an additional X chromosome in females. The associated symptoms and physical features vary greatly, some females may have no symptoms or very mild symptoms and may go undiagnosed. Other women may have a wide variety of different abnormalities, like learning disabilities and delayed development of speech and language skills, seizures or kidney abnormalities. Also called trisomy X.
a sex chromosome aneuploidy, which is caused by the presence of an extra Y chromosome in males. Affected individuals are usually very tall, often have learning disabilities and behavioural problems. Most males with 47,XYY syndrome have normal sexual development and are able to father children. This condition occurs in about 1 in 1,000 newborn boys. Also called "double Y syndrome".


Professional organisations

Patients resources


NIPT references list