Obstetrics: Antenatal screening and appointments

Question 1

When are women screened for Rhesus status and how are they managed?

Answer 1

1. Booking visit - blood sample sent for Ab screening to identify blood group and Rhesus status
2. 28 wks - mother is screened again for rhesus status

Anti-D prophylaxis:

• Given at 28wks and 34wks
• Given within 72 hours post birth in all women not previously identified as being RhD following +ve result from cord sample

Transfusion - only if foetus is anaemic

Question 2

What are the summary of dates for the various antenatal appointments?

Answer 2

8-12 wks - Booking visit
11+0 - 13+6 wks - Dating scan and Combined test
18 - 20+6 wks - Anatomy scan (anomaly)
25-26 wks - urinalysis, SFH, BP
28 wks - 2nd screen for anaemia and RhD; 1st dose of anti-D
34 wks - 2nd dose of anti-D
36 wks - check lie, presentation and engagement
41wks - close surveillance; cervical sweep offered

Question 3

What are the dates for trisomy screening?

Answer 3

The following tests screen for trisomy 21 (Down’s), 18 (Edward’s) and 13 (Patau’s)

1. 11+0-13+6wks = Booking visit + Quadruple test (85%)
   - Nuchal translucency, PAPP-A (low), HCG (raised)
2. > 11 wks = CVS
   - sample taken from placenta
3. 11-16wks (can be up to 20) = Quadruple test (80%)
   - HCG, Inhibin-A, AFP, Unconjugated bilirubin
4. > 15wks = Amniocentesis
   - sample taken from amniotic fluid
5. NIPT = non-invasive pre-natal testing (99%)
   - privately funded