Antepartum

Question 1

How to screen for thalassemia?

Answer 1

Both parents MCV<80
Alpha: blood film (inclusion bodies), IC strip
Beta: HPLC x HbA2

+ve -> carrier status
Both -ve -> alpha genotyping

Question 2

What is the etiology of Down’s syndrome?

Answer 2

Non-dysjunction (meiosis I of oocytogenesis)
Robertsonian translocation
Mosaicism

Question 3

What are the prenatal features of Down’s syndrome?

Answer 3

AVSD, duodenal atresia
1st trimester: increased NT, x nasal bridge, TR, reversed a wave in ductus venosus
2nd trimester: echogenic bowel/liver/cardiac focus, dilated pelvis, short femur

Question 4

What to do if USG screening result is abnormal for Down’s?

Answer 4

CVS b/c lower risk of placental mosaicism & earlier Dx

Question 5

What to do if NIPT screening is abnormal for Down’s syndrome?

Answer 5

Amniocentesis b/c possibility of placental mosaicism causing +ve NIPT

Question 6

What are the traditional screening methods for Down’s syndrome?

Answer 6

1st trimester DSS1/OSCAR: age, NT, b-HCG (high), PAPP-A (low)
2nd trimester quadruple test: b-HCG & inhibin (high), uE3 & AFP (low)

Question 7

When is NT measured?

Answer 7

11-13w

CRL 45-84mm

Question 8

What is the cutoff for NT?

Answer 8

3mm

Question 9

What are the limitations of NIPT?

Answer 9

FP: placental mosaicism, vanished twin
FN: when fetal DNA is <4%
Others: self-financed, x Dx, only detects T21/18/13/Turner

Question 10

What is the risk of fetal loss for CVS & amniocentesis?

Answer 10

0.2-0.3% for CVS & amniocentesis

Question 11

Features of CVS?

Answer 11

Timing: 10-14w
Higher risk of FP
Req LA (thicker needle, more painful)

Question 12

Features of amniocentesis?

Answer 12

Timing: 15-20w
Lower risk of FP
x req LA (thinner needle, less painful)

Question 13

How to analyze prenatal invasive tests?

Answer 13

Karyotyping (long time)
Quantitative fluorescence PCR (only T21, 18, 13, XY)
Prenatal BoBs assay (T12, 18, 13, XY, 9 common microdeletion syndromes)
Array comparative genomic hybridization / fetal DNA chip (submicroscopic chromosomal aberrations)

Question 14

How to screen for GBS?

Answer 14

Vaginal rectal swab at 36-38w

Question 15

What are the indications of GBS ABX PPx?

Answer 15

Known carrier at onset of labour, IOL, ROM

Unknown status if <37w, >38C, ROM>18hr

Question 16

What is the regimen of ABX PPx for GBS?

Answer 16

IV ampicillin (2g bolus then 1g Q4H until delivery)

• Allergic to penicillin: clindamycin
• Resistant to clindamycin: vancomycin

Question 17

How to do Rhesus screening?

Answer 17

Check mum’s Rh status
If +ve -> x abx
If -ve
- Check mum’s Anti-D Ab now and again at 28w
- Check dad’s Rh status -> if -ve (x ABX), if +ve / unknown (give ABX)

Question 18

How to manage Rhesus D -ve mothers?

Answer 18

PPx by IM Anti-D Ab at 28w