First trimester screening

Question 1

What is the risk of Down Syndrome in women >35 years old?

Answer 1

1/300

Question 2

Describe the purpose of genetic screening in pregnancy

Answer 2

Gives the risk profile for trisomy 13/18/21 to allow diagnostic testing to be considered

Question 3

What is the most common trisomy detected on first trimester screening?

Answer 3

Trisomy 21 –> ~50%

Question 4

What are the 3 types of genetic screening in pregnancy?

Answer 4

• MSS1
• MSS2
• NIPT

Question 5

Describe the MSS1

Answer 5

The MSS1 is a first trimester screening tests that detects the risk of having a pregnancy affected by a chromosomal abnormality (trisomy 13/18/21)

It involves:
* NT scan at 11-12+6 weeks
* Bloods = PAPP-A and beta-hCG
* Maternal age

Sensitivity 85% and specificity 95% (false positive rate 5%)

Question 6

Describe the MSS2

Answer 6

The MSS2 is a 2nd trimester screening test performed at15-20 weeks that detects the risk of having a pregnancy affected by a chromosomal abnormality (trisomy 13/18/21)

It involves:
* Bloods = AFP, beta-hCG, inhibin A, unconjugated oestradiol
* Maternal age

Sensitivity 75% and specificity 95% (false positive rate 5%)

Question 7

Describe the NIPT test

Answer 7

NIPT can be performed anytime >10 weeks and involves isolation of cfDNA from maternal blood

Sensitivity and specificity 99%

Not currently funded ~$600-700

Question 8

Describe different methods of diagnostic testing for chromosomal abnormalities

Answer 8

Diagnostic testing requires extraction of fetal DNA to assess with FISH or cell culture
* CVS –> from 11 weeks
* Amniocentesis –> from 15 weeks

Both tests carry a risk of miscarriage of ~1%