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Prenatal Testing Flashcards

1
Q

What percentage of babies born in Victoria have a birth defect?

A

4% (including stillbirths)

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2
Q

Why is prenatal testing done?

A

allows couple the choice to terminate, allows couple to psychologically prepare, allows health care team to prepare, gives reassurance with a normal result

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3
Q

What is a prenatal screening test?

A

a test which identifies which women are at risk of having a child with birth defect - the tests are non invasive and are not definitive

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4
Q

What is measured in the first trimester combined screening test?

A

blood taken at 10 weeks which measures PAPP-A and the beta subunit of hCG and an ultrasound to determine nuchal translucency, nasal bone and crown rump length

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5
Q

What is the cut-off for T21 for first trimester combined screening?

A

1 in 300

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6
Q

What is the cut off for T18 for first trimester combined screening?

A

1 in 175

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7
Q

What is the detection rate for T21 in first trimester combined screening?

A

93%

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8
Q

What is measured in second trimester maternal serum screening test?

A

blood taken at 14-20 weeks which measures 4 biochemical analytes - beta hCG, inhibin, oestriol and alpha fetal protein

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9
Q

In second trimester maternal serum screening what are the analytes results that give an increased risk for trisomy 21?

A

low alpha fetal protein and oestriol and high hCG and inhibin

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10
Q

In second trimester maternal serum screening what are the analytes results that give an increased risk for neural tube defects?

A

raised alpha fetal protein

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11
Q

What is the cut off for T21 for second trimester maternal serum screening?

A

1 in 250

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12
Q

What is the cut off for T18 for second trimester maternal serum screening?

A

1 in 200

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13
Q

What is the cut off for neural tube defects for second trimester maternal serum screening?

A

> 2 MoM

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14
Q

What is the detection rate for T21 in second trimester maternal serum screening?

A

85%

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15
Q

What is the detection rate for neural tube defects in second trimester maternal serum screening?

A

93%

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16
Q

What is genetic carrier screening?

A

a test to see if parents are carriers for autosomal recessive conditions

17
Q

What women are offered invasive diagnostic prenatal testing?

A

women with an increased risk screening result, women of advanced maternal age, couples who are known carriers

18
Q

What are the two methods of diagnostic prenatal testing?

A

chorionic villus sampling and amniocentisis

19
Q

What is chorionic villus sampling?

A

a needle is inserted into placental tissue under ultrasound

20
Q

What is amniocentisis?

A

a needle is inserted under ultrasound and 20ml of amniotic fluid is collected

21
Q

What tests are done with the sample collected from CVS or amniocentisis?

A

FISHing and karyotyping and chromosomal microarray

22
Q

What is FISHing for chromosomes?

A

fluorescent in situ hybridisation - fluorescent probes are attached to chromosomes to count the number of chromosomes - 3 colour FISH is X,Y and 21 and 5 colour FISH is X, Y, 21, 18 and 13

23
Q

Why does karyotyping take a long time?

A

because cells need to be grown in culture for 2 weeks

24
Q

What is reciprocal translocation?

A

exchange of material between two non identical chromosomes

25
Q

What is a Robertsonian translocation?

A

a translocation between the two long arms of two acrocentric chromosomes joined at or near the centromere (13,14,15,21 and 22)

26
Q

What percentage of Down’s syndrome cases are due to an unbalanced translocation?

A

5% - of which some are due to inheritance from a parent with a balanced translocation

27
Q

What is a chromosomal microarray?

A

a genetic test which involves probes along the chromosomes and then hybridisation and by comparing copy number variations it can be determined whether there may be a gain or loss of genetic material - although wont detect a balanced translocation

28
Q

What is pre implantation genetic diagnosis?

A

genetic testing (FISH and chromosomal microarrays) done on a 3 day old zygote before implantation for IVF

29
Q

What is non invasive pre natal screening?

A

tests the cell free fetal DNA or RNA in the maternal blood for genetic abnormalities using MPS - still not officially diagnostic and would have to be followed up with a diagnostic test

Reproduction (21 decks)

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