Foetal screening techniques

Question 1

Foetal screening techniques

Answer 1

Foetal screening techniques are medical tests done during pregnancy to check the health and development of the unborn baby (foetus).

These tests look for any genetic disorders, birth defects, or health problems.

Question 2

Ultrasound

Answer 2

Inaudible, high frequency sound waves to produce an image of the foetus.

A probe is placed on the abdomen of the pregnant women, and the sound-waves are reflected by foetal tissues to obtain a visual ‘echo’ of what is inside the uterus.

Doctor then feeds these reflected sound waves into the computer.

Images produced by ultra sound can be used to monitor the growth and development of the foetus.

Question 3

Information ultrasound gives

Answer 3

1. confirming pregnancy
2. estimating the stage of pregnancy
3. determining the number of foetuses.
4. identifying abnormalities of cervix or uterus.
5. Monitoring the growth of the foetus
6. determining the gender of the foetus
7. evaluating the anatomy of the foetus.
8. genetic screening.

Question 4

Ultrasound limitations

Answer 4

cannot diagnose all abnormalities, therefore further testing may be required.

• genetic or chromosomal conditions.

Question 5

Genetic analysis

Answer 5

1. amniocentesis
2. chorionic villus sampling

These test can be used to examine the foetus’s chromosomes to detect defective, missing or additional chromosomes.

Question 6

Ammiocentesis

Answer 6

Involves ultrasound to guide a needle through the wall of the abdomen into the abdominal cavity.

Approx. 10-20ml of amniotic fluid is taken out.

Fluid contains cells from the foetus which are examined for biochemical defects and for abnormalities in the number of chromosomes or in the chromosome structure.

Usually done during 16 - 20 weeks of pregnancy… time when foetus is floating in about 130ml of amniotic fluid.

Question 7

Risks and defects of amniocentesis

Answer 7

Small risk of infection, miscarriage or damage to the baby, therefore only performed on women who are thought to be at higher risk of delivering a child with birth defect.

Disorders… down syndrome, cystic fibrosis, neural tube defects such as spina bifida.

Question 8

Chorionic villus sampling

Answer 8

Cvs obtains a specimen of foetal cells from one of the foetal membranes, the chorion.

Cells are examined in a similar way to amnioncentesis.

Important if a birth defect is involved that may require termination of the pregnancy.

disadvantages, risk of miscarriage (2%), cannot detect spina bifida.

testing takes place 9-19 weeks of pregnancy and is used to detect genetic disorders and biochemical abnormalities.

Question 9

Blood test

Answer 9

A blood test of the mother’s blood is a non invasive prenatal test that is possible due to some of the baby’s DNA passing into the mothers blood

This is a screening test not diagnostic as it is able to identify if there is an increased chance of the baby having a disorder.

can detect all the syndromes and is available after 10 weeks of gestation.

If an increases chance of abnormality then, CVS and amniocentesis would be recommended to confirm the diagnosis.

Question 10

Foetal monitoring

Answer 10

regular recording of the baby’s heart rate in order to detect indicators of stress.

Monitoring usually takes place during labour and birth using ultrasound and electrocardiography to examine foetal heart rates and mother’s condition.

aim: to identify any risks of injury to the foetus so that appropriate action can be taken.

also allows information of any risk of oxygen deficiency occuring.

Question 11

Fetoscopy equiptment

Answer 11

Used to gain info about foetus in uterus.

1. sthethoscope - listens to the foetus’s heartbeat.
2. Fibre-optic scope - looks directly at the foetus through a small, telescope like instrument with a diameter about the size of a hypodermic needle.

inserted into the uterus through the abdominal wall.

Detection of cleft lip and palate, missing or abnormal ears, absent limbs

Question 12

Fetoscopy use time

Answer 12

used during foetal surgery, is a risky difficult procedure that is only performed by a specialist doctor, usually after an ultrasound has indicated the possibility of foetal abnormalities such as spina bifida or duchenne muscular dystrophy.

Question 13

Foetal blood sampling for?

Answer 13

blood may be sampled to…

1. diagnose chromosomal abnormalities
2. diagnose foetal anaemia
3. check foetal oxygenation
4. identify infections
5. give medicaitons

Question 14

Where is foetal blood sampling taken from

Answer 14

1. the umbilical cord via percutaneous umbilical cord blood sampling (PUBS), where a needle is inserted through the abdominal wall and uterus into the umbilical vein.
2. A foetus blood vessels, usually the liver or the heart via a fetoscope.

Question 15

Disadvantages for foetal blood sampling

Answer 15

High risk or miscarriage (1-2%), risk of infection, blood loss and premature rupture of the amniotic sac.

Question 16

Biochemical analysis

Answer 16

Technique used to detect phenyulketnuria (PKU) either by testing blood or urine. searching for proteins that uphold these diseases.

Question 17

DNA PROBES

Answer 17

More recent innovation that enable the detection of a range or genetic disorders, such as duchenne muscular dystrophy and thalassarmia.

probs are based on recombinant DNA technology

Question 18

how do DNA PROBES work

Answer 18

A segment of DNA is used that is strucutrally identical to the gene being tested. some of the units in DNA segments are ‘labelled’ with a dye or radioscope.

This DNA probe is then joined to the gene.

1. Normal gene, the DNA probe joins with the DNA segments with which it is structurally identical and shows them up.
2. Abnormal gene, it does not show up and is identifiable as a gap in DNA being tested