Prenatal testing

Question 1

What are the normal pregnancy scans done?

Answer 1

Nuchal scan and anomaly scan.

Question 2

How is a nuchal scan done?

Answer 2

Ultrasound is used to see thickness of fluid at back of fetal neck. A thickness greater than 3mm in associated with chromosomal abnormalaties.

Question 3

What might a nuchal scan be paired with?

Answer 3

Combined with maternal blood markers and age.

Question 4

When is nuchal scan done?

Answer 4

Done at 12 weeks.

Question 5

How is an anomaly scan done?

Answer 5

Ultrasound to see for structural anomalies in organs and bones.

Question 6

What non invasive prenatal testing can be done?

Answer 6

Cell free fetal DNA screening.

Question 7

How is cell free fetal DNA screening done?

Answer 7

Analysis of fetal DNA in maternal bloodstream.

Question 8

When is cffDNA screening done?

Answer 8

9 weeks.

Question 9

In cffDNA screening what is looked at?

Answer 9

Sex determining region (if there is an x linked condition in family). Test for aneuploidy (invasive to confirm).

Question 10

Pros of cffDNA screening?

Answer 10

Offered early during pregnancy. No increased risk of miscarriage.

Question 11

Limitations of cffDNA screening?

Answer 11

Can’t be used in multiple pregnancies. Can’t be used with woman with high BMI.

Question 12

Two types of invasive testing?

Answer 12

Chorionic villus sampling and amniocentesis.

Question 13

When is chorionic villus sampling done?

Answer 13

11-14 weeks.

Question 14

How is chorionic villus sampling done?

Answer 14

Needle through abdomen or vagina to obtain chorionic villus cells.

Question 15

Risks of chorionic villus sampling?

Answer 15

1-2% risk of miscarriage. Infection. Rhesus sensitisaton

Question 16

When is amniocentesis done?

Answer 16

16 weeks.

Question 17

How is amniocentesis done?

Answer 17

Sample of amniotic fluid is obtained.

Question 18

Risks of amniocentesis?

Answer 18

Up to 1% chance of miscarriage. Infection. Rhesus sensitisation

Question 19

In invasive testing what is fetal DNA tested for?

Answer 19

Genetic disorder or chromosomal abnormality.

Question 20

How is CGH array done?

Answer 20

DNA sample compared to control using computer. Picks up microdeletions and duplications in DNA.

Question 21

How is prenatal exome done?

Answer 21

Screening of coding region.

Question 22

If structural anomalies are detected on prenatal ultrasound what test can be done?

Answer 22

Prenatal exome sequencing.

Question 23

In preimplantation genetic diagnosis when are the cells removed for testing for the genetic condition in the family?

Answer 23

Day 5. Blastocyst stage.

Question 24

Criteria for PGD?

Answer 24

Female partner is under age 39
Female partner has a BMI of 19-30
Both partners are non-smokers