Prenatal diagnosis

Question 1

Why are prenatal diagnostics valuable?

Answer 1

Because it enables:
Option of termination of pregnancy in conditions with poor prognosis.
Appropriate counselling in structural problems.
Planning for pregnancy and delivery at an appropriate place.
Prenatal therapy.

Question 2

What combination of tests are part of the screening with best detection rate and lowest false positive rate for Down syndrome?

Answer 2

Maternal age (MA). 
Nuchal translucency (NT). 
Nasal bone length (NB).
Biochemical serum markers: PAPP-A and beta-hCG. 
(DR 95 % and FPR 2 %.)

Question 3

What are available methods of prenatal testing?

Answer 3

Amniocentesis.
Chorionic villus sampling.
Fetal blood sampling.
Non-invasive prenatal testing.

Question 4

What is it important to inform the patient of before performing prenatal testing?

Answer 4

They must give consent.
National and local risks.
Analysis of the sample.
Accuracy of particular lab test being performed.
Culture failure rates.
Reporting time.
Method of communication of results.
Indications for seeking medical advice following the test.

Question 5

What are contraindication for performing invasive prenatal testing?

Answer 5

Invasive prenatal procedures should not be carried
out without reviewing available blood-borne virus
screening tests.

In the third trimester prenatal testing cannot be carried out in women with HCV and HBV.

Question 6

At what time of gestation can chorionic villus sampling be done?

Answer 6

After 10+0 weeks.

Question 7

At what time of gestation can amniocentesis be done?

Answer 7

It it usually performed after week 15.
(Amniocentesis before week 14 is associated with a higher fetal loss rate as well as an increased incidence of fetal talipes and respiratory morbidity.)

Question 8

Is local anesthetics commonly used when performing amniocentesis?

Answer 8

It could be used. However, local anesthetic did not reduce pain scores reported by women undergoing amniocentesis.

Question 9

What aneuploidies is the QF-PCR commonly used to test for?

Answer 9

Trimosy 21, 13 and 18.

Question 10

What type of gene abnormality is a chromosomal microarray / comparative genome hybridization used to find?

Answer 10

CGH compares a ʻnormalʼ genome with a patient genome. The test picks up extra or missing bits of chromosomes, but not single gene mistakes.

Question 11

Cell-free DNA in the maternal circulation can have either maternal or fetal origin. How much of the cell-free DNA usually stems from the fetus?

Answer 11

10-20 %. (Because both the placenta and fetus is mitotically active.)

Question 12

What is the detection rate (DR) and false positive rate (FPR) for trisomy 21 using cf-DNA?

Answer 12

DR 99 %.

FPR 0,08 %.

Question 13

True or false: Fetal DNA is extracted from maternal blood.

Answer 13

Combined maternal and placental DNA is processed. Although possible, fetal DNA is not separately identified.

Question 14

Why is there still use for ultrasound when we can use NIPT?

Answer 14

Ultrasound is necessary for:
Dating the pregnancy.
Confirm single and intrauterine pregnancy.
Detect major structural abnormalities.

Question 15

Why cannot NIPT replace amniocentesis?

Answer 15

NIPT is a very good SCREENING test, but there are false positives (more common) and false negatives (less common).

Question 16

What are disadvantages of NIPT?

Answer 16

It is expensive.
Some test results are ambiguous.
The range of abnormalities currently detected is less than that with invasive testing and micro-array.