Prenatal Screening Or Diagnosis: From 1 Different Sources
Prenatal screening of fetal abnormalities may be the result of screening tests carried out on most or all pregnant women, or as the result of speci?c diagnostic tests performed to detect speci?c conditions. Prenatal diagnosis is important as it will identify babies who might need medical or surgical treatment before or soon after birth. In addition, it may also detect severe abnormalities for which parents might decide to have a therapeutic ABORTION.
ULTRASOUND scanning is probably the most widely used diagnostic tool in obstetric practice. It can detect structural abnormalities such as SPINA BIFIDA and CLEFT PALATE and even cardiac and renal problems. A series of scans can assess whether the baby is growing at a normal rate; ultrasound may also be used to assist with other diagnostic tests (e.g. AMNIOCENTESIS – see below).
Tests on the mother’s blood can also diagnose fetal abnormalities. Alphafetoprotein (AFP) is produced by babies and ‘leaks’ into the AMNIOTIC FLUID and is absorbed by the mother. In spina bi?da and other neural-tube defects there is increased leakage of AFP, and a blood test at 16 weeks’ gestation can detect a raised level which suggests the presence of these abnormalities.
The triple test, also performed at 16 weeks, measures AFP and two hormones – HUMAN CHORIONIC GONADOTROPHIN and unconjugated OESTRADIOL – and is used in diagnosing DOWN’S (DOWN) SYNDROME.
Amniocentesis involves inserting a needle through the mother’s abdominal wall into the uterus to remove a sample of amniotic ?uid at 16–18 weeks. Examination of the ?uid and the cells it contains is used in the diagnosis of Down’s syndrome and other inherited disorders. The test carries a small risk of miscarriage.
Chorionic villus sampling may be used to diagnose various inherited conditions. A small amount of tissue from the developing PLACENTA is removed for analysis: this test has the advantages of having a lower incidence of miscarriage than amniocentesis and is carried out at an earlier stage (9–13 weeks).
Analysis of a blood sample removed from the umbilical cord (cordocentesis) may diagnose infections in the uterus, blood disorders or inherited conditions.
Direct observation of the fetus via a viewing instrument called a fetoscope is also used diagnostically and will detect structural abnormalities.
Most tests have a recognised incidence of false positive and negative results and are therefore usually cross-checked with another test. Counselling of the parents about prenatal tests is important. This allows them to make an informed choice which may not necessarily involve terminating the pregnancy if an abnormality is found. (See PREGNANCY AND LABOUR.)
The process of determining health status and the factors responsible for producing it. It may be applied to an individual, family, group or community. The term is applied both to the process of determination and to its findings. See also “principal diagnosis”.... diagnosis
A list of the possible diagnoses that might explain a patient’s symptoms and signs, and from which the correct DIAGNOSIS will be extracted after further investigations.... differential diagnosis
The use of procedures and measures to identify and differentiate apparently well persons who have a disease or condition or a high risk thereof from those who probably do not have the disease or condition.... screening
The screening of apparently healthy people to identify those who may have treatable diseases. Cervical smears are done when screening women to detect if they have cancer or precancer of the neck of the womb (cervix). Newborn babies are screened for hip dislocation. Screening tests are not designed to diagnose individual persons, but rather to divide a population into a large number at low risk and a small number at high risk of a condition. This allows clinicians to concentrate on a sub-section of the population. All screening tests produce false negative and false positive results, a problem often misunderstood by those at the receiving end. Factors to be assessed when planning screening procedures include the severity, frequency and distribution of the disease, and the availability and e?ectiveness of treatment. Convenience, safety, sensitivity and cost should also be assessed. In the United Kingdom the government has supported the extension of screening procedures for breast cancer, cervical cancer, hypertension and diabetes. (See PREVENTIVE MEDICINE.)... screening test
A set of investigations aimed at the early detection of breast cancer. It includes self-screening by monthly examination of the breasts, and formal programmes of screening by palpation and mammography in special clinics. In the UK the NHS o?ers regular mammography examinations to all women between 50 and 64 years of age; in 1995–6, 1.1 million women were screened – 76 per cent of those invited. More than 5,500 cancers were detected – 5.3 per 1,000 women screened.... breast screening
The use of information technology to assist health care professionals in diagnosis. This usually involves a dialogue between a computer system and a clinician. The systems are generally regarded as support systems for clinicians; the final responsibility for decision-making resides with the clinician.... computer-assisted diagnosis
A system used for payment under prospective payment systems. It classifies treatments by diagnosis, measuring the relative complexity of a hospital procedure and accounting for the resources used in the procedure. The system accounts for principal diagnosis, secondary diagnosis, surgical procedures, age, sex and presence of complications.... diagnosis-related group
1 Represents classes of hospital patients with similar clinical characteristics. DRGs form a clinical grouping system which describes hospital discharges according to medical condition. 2 A system used for payment under prospective payment systems. It classifies treatments by diagnosis, measuring the relative complexity of a hospital procedure and accounting for the resources used in the procedure. The system accounts for principal diagnosis, secondary diagnosis, surgical procedures, age, sex and presence of complications.... diagnosis-related group (drg)
The medical condition that is ultimately determined to have caused a person’s need for medical care. The principal diagnosis is used to assign every person to a diagnosis-related group. This diagnosis may differ from the admitting and major diagnoses. See also “diagnosis”.... principal diagnosis
Tests to detect early signs of cancer in groups of people who are susceptible to cancer because of their age, occupation, lifestyle, or genetic predisposition. Tests for cancers of the cervix (see cervical smear test), breast (see mammography), bladder, and colon have proven to be effective.... cancer screening
The period of pregnancy before childbirth.... prenatal
see prenatal diagnosis.... antenatal diagnosis
*screening tests to detect the presence of precancerous changes in the cervix (neck) of the uterus (see cervical intraepithelial neoplasia). *Cervical smears are the standard first-line screening tools in most countries: screening programmes based on the traditional Papanicolaou (Pap) test have been mostly superseded by *liquid-based cytology. *Colposcopy is indicated when abnormal cells (*dyskaryosis) are detected.... cervical screening
a screening tool for young people under the age of 21 to identify alcohol and drug use. The first part consists of three questions about drug or alcohol use over the past year. Participants giving positive answers to two or more questions proceed to the second part (from which the name derives), which contains six questions with the key words car, relax, alone, family/friends, forget, trouble, used to assess the need for further input.... crafft screening test
the coexistence of a severe mental disorder with a *substance misuse disorder.... dual diagnosis
see MUST.... malnutrition universal screening tool
*screening tests carried out on newborn babies to detect diseases that appear in the neonatal period, such as phenylketonuria (see Guthrie test). If these diseases are detected early enough, treatment may be instigated before any irreversible damage occurs to the baby.... neonatal screening
(NIPD) see prenatal diagnosis.... noninvasive prenatal diagnosis
a technique for improving the sensitivity and specificity of bladder cancer diagnosis at cystoscopy using a light-sensitive agent. This agent is instilled into the bladder, taken up by the epithelial cells, and converted into a porphyrin that accumulates only in malignant and premalignant cells. It fluoresces under light of a specific wavelength and is thus highlighted against normal bladder mucosa.... photodynamic diagnosis
(PGD) a diagnostic procedure carried out on embryos at the earliest stage of development, before implantation in the uterus. Access to these early embryos requires the *in vitro fertilization of egg cells: three days after fertilization one or two cells are aspirated from the six-cell embryo; alternatively, tissue is removed from an embryo at five or six days, when it has reached the *blastocyst stage. Isolated cells can then be genetically analysed, allowing the transfer of selected embryos to the mother. One of the major applications of PGD is for the detection (using the *FISH technique) of chromosomal abnormalities, especially *aneuploidies (e.g. Down’s syndrome); the procedure is used mainly in women who have had repeated miscarriages or have failed to achieve pregnancy after several IVF treatment cycles, which could be due to the presence of such abnormalities in the embryo. PGD can also be used to detect defective genes responsible for hereditary disorders (e.g. the commonest form of cystic fibrosis, Huntington’s disease) and genes associated with susceptibility to certain cancers. When a defect is detected, *genetic counselling is offered.... preimplantation genetic diagnosis
(antenatal diagnosis) diagnostic procedures carried out on pregnant women in order to detect the presence of genetic or other abnormalities in the developing fetus. Ultrasound scanning (see ultrasonography) remains the cornerstone of prenatal diagnosis. Other procedures include chromosome and enzyme analysis of fetal cells obtained by *amniocentesis or, at an earlier stage of pregnancy, by *chorionic villus sampling (CVS). Noninvasive prenatal diagnosis involves a blood test to analyse cell-free fetal DNA in maternal blood. It can be performed during the first trimester and is used for fetal rhesus (Rh) determination in Rh-negative mothers, fetal sex determination in pregnancies at risk of sex-linked disorders, and for some single-sex gene disorders (e.g. achondroplasia). Compare prenatal screening.... prenatal diagnosis
*screening tests carried out to estimate the risk of chromosomal or other abnormalities being present in a developing fetus. They include blood tests to measure levels of *human chorionic gonadotrophin (hCG), *PAPP-A, *alpha-fetoprotein (AFP), inhibin (see activin), and *unconjugated oestriol (uE3) (see also triple test) and also ultrasound scanning for the presence of soft markers (see ultrasound marker; nuchal translucency scanning). If the results indicate a high risk of abnormalities being present, a diagnosis may be confirmed by more invasive procedures (see prenatal diagnosis).... prenatal screening
the use of an image intensifier to produce *real-time imaging during an X-ray examination on a TV monitor. It is widely used in angiography and *interventional radiology to guide procedures. See videofluoroscopy.... x-ray screening
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