Mrs X Para 2+1 with dichorionic diamniotic twins.
Anti-D+G present
Anti-D quantitation levels at 13+2 and 29+3 weeks were 21IU/mL-1 and 330IU/mL-1 respectively.
Mum O RhD Positive rr, Dad A Rh D Positive R2Ro
Twin 1: A RhD Positive DAT 4+, did not go over 1.5MoMs on middle cerebral artery Doppler peak systolic velocity surveillance and did NOT require IUT. Postnatally only required top up Tx’s
Twin 2: O RhD Positive R2r DAT 4+. required three intrauterine transfusions. Postnatally required Exchange Tx, IVIg and phototx and serial top-ups
Although both twins in this case were RhD positive only one was severely affected.
What are the possible reasons / theories to explain this disparity?
According to Mollison there are 3 circumstances the fetus may be unaffected or only mildly affected despite a strong positive result in a cellular bioassay. These are:
1. Fetus Rh D Negative
2. Presence of Fc receptor blocking antibodies
3. Diminished transport of maternal IgG to the fetus
Are there any other suggestions theories or advice?