Ante- and postnatal screening Flashcards
How is the health of a pregnant woman and her developing foetus monitored?
using a variety of techniques and tests
What does antenatal screening do?
identifies the risk of a disorder so that further tests and prenatal diagnosis can be offered
What can several methods of antenatal screening be used to do?
identify the risk of a foetus inheriting a genetic disorder or chromosomal abnormality
What are the 2 types of antenatal screening tests that can be carried out during a pregnant woman’s antenatal appointments?
ultrasound imaging biochemical tests (blood tests)
What is an ultrasound scanner held against?
a pregnant woman’s abdomen
What does an ultrasound scanner do?
it picks up high-frequency sounds that have bounced off the foetus and then converts these sounds into ultrasound image on the computer screen
What are the 2 types of ultrasound scans and when are they performed?
dating scan - between 8-14 weeks
anomaly scan - between 18-21 weeks
How safe are ultrasound scans?
they are completely harmless, have no known side effects on mothers or babies, and can be carried out at any stage of pregnancl
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What is the dating scan used to do?
determine the stage of the pregnancy (gestational age assessment) and to calculate the date when the baby is due to be born.
What are dating scans usually used in conjunction with?
biochemical tests for marker chemicals
What can be detected during the dating scans and give an example?
some abnormalities can be detected, such as neural tube defects e.g. spina bifida
What can happen if a dating scan takes place between weeks 11-14?
it can be combined with a blood test and measuring of the fluid at the back of the baby’s neck (nuchal translucency)
What is a nuchal translucency?
measuring of the fluid at the back of the baby’s neck
If a dating scan is combined with a blood test and the fluid in the tissue at nape of the baby’s neck is measured what can this accurately screen for?
down’s syndrome, however the test will only be carried out with the mother’s permission
What does an anomaly scan allow?
a check to be made for the presence of any physical abnormalities in the foetus e.g. cleft lip
What parts of the body are looked at in detail in the anomaly scan?
the baby’s bones, heart, brain, spinal cord, face, kidneys and abdomen
What will sonographer look for specifically?
for 11 conditions, some of which are very rare
When a woman is pregnant, her body naturally undergoes many physiological changes. How can these changes be monitored?
by biochemical tests
How can some medical conditions be indicated?
by the presence of certain marker chemicals in the blood and urine.
What happens to the concentration of marker chemicals throughout pregnancy?
it varies
What chemical marker is frequently analysed during pregnancy?
Human Chorionic Gonadtrophin (HCG)
What is HCG?
a hormone which is detected in the blood and urine following implantation of an embryo. It is also the basis of early pregnancy tests
Describe the levels of HCG in a normal pregnancy?
the level of HCG increases during weeks 6-10 and then decreases to a steady low level later in gestation
Describe the level of HCG in a foetus that has down’s syndrome?
the level of HCG increases during weeks 6-10 and then remains at a level
What are the 3 tests taken to monitor the health of the mother and the developing foetus on a regular basis?
thyroid function renal function liver function (also, blood pressure)
What is a false positive?
if a marker chemical was measured at the wrong time during pregnancy and found to be high. This could lead to diagnosing a fetus with a condition that they don’t have
What is false negative?
suggests a fetus doesn’t have a condition when in fact he/she does. It is for this reason that the times chosen for biochemical tests are closely synchronised with the data from ultrasound dating scans.
What is a diagnostic test?
a definitive test that will show whether a developing actually has the condition (whereas screening tests only assess the risk of a condition)
When would certain diagnostic tests be offered to pregnant women (3)
if there is evidence of a potential problem as a result of earlier routine screening tests (NT scan)
If there is a family history of a harmful genetic disorder.
The mother belongs to ‘high-risk’ category e.g. smoke, drugs, alcohol
What are the 2 common types of diagnostic tests?
Amniocentesis
Chorionic villus sampling
What do both Amniocentesis and Chorionic villus sampling rely on?
producing a karyotype
What is a karyotype?
a visual representation of an individual’s chromosome complement where the number of chromosomes,
their arrangement, size and structure can be analysed
What the analysis of a karyotype be carried out on ?
on a sample of blood, chorionic villi or other material containing cells
When preparing a karyotype, what happens to the sample of cells collected from a sample of blood, chorionic villi or other material containing cells?
they are cultured, the karyotype image is prepared by staining the chromosomes of a cell with a dye and photographing them down a microscope. The image is then analysed using a specialised computer software which arranges the chromosomes in order of size.
What can amniocentesis assess?
whether an unborn baby could develop, or has developed, an abnormality or serious genetic condition e.g. Down’s syndrome, spina bifida or sickle cell anaemia
When is amniocentesis usually carried out?
during weeks 14-16 of pregnancy if necessary and is completely voluntary
What does amniocentesis involve?
the removal of amniotic fluid which surrounds the fetus in the womb. From the fluid, foetal cells are collected and cultured before being examined under the microscope.
How can cell samples which are obtained during amniocentesis be used to assess the health of the developing baby and diagnose potential problems?
by preparing and analysing a karyotype of the baby’s chromosomes
What are the advantages of amniocentesis?
prenatal diagnosis possible
detects neural tube defects
What are the disadvantages of amniocentesis?
small risk of miscarriage (less than CVS)
gives results later in pregnancy
When can CVS take place?
as early as 8 weeks
What is CVS offered during pregnancy for?
to check for genetic disorders e.g. Down’s syndrome