Hello 

Patient has developed antiD in first pregnancy at around 32 weeks and her quantification level was 1.0 IU/ml.

In 2nd pregnancy her booking blood at (12 weeks) antibody screening was negative.  At 15 weeks sample sent for fetal genotype (FDS). On this Report received inconclusive due to all Anti D.

Because patients was on file for historical antibody therefore sample sent for quantification  in 2nd pregnancy and Report received antibody not quantified since it reacted weakly in enzyme IAT only. 

My understanding standing is if patients once developed Allo antiD her titre level does not go down. Why was her antibody screen was negative in 2nd pregnancy at 12 weeks?

Just my guess, is there any possibilities of fetus D pos cells bind partof the antibodies?

This may not be easy/possible to do, but have you checked that the patient had not been given a very large dose of anti-D immunoglobulin during her first pregnancy?  It is not totally unknown for a woman to develop an allo-anti-D in her first pregnancy, although it is incredibly rare, but, if the patient had an abdominal trauma, she could well have been given a very large dose of anti-D immunoglobulin.

This may explain why her antibody screen was negative at 12 weeks of gestation in her second pregnancy.

There is also the (vague) possibility that the anti-D in the patient's circulation first pregnancy MAY have been a mis-identified anti-LW.

I must confess that I am slightly at a loss as to why the 15 week sample could not be used for foetal RHD genotyping, leading to a prediction of the D antigen expression on the foetal red cells, unless all the foetal red cells had been cleared from the maternal circulation.  If this is the case, there are still other ways of obtaining foetal DNA (albeit more dangerous), such as foetal reticulocytes in the amniotic fluid.  If the "anti-D" is only "enzyme-reactive", it is true that it would be impossible to quantify, but it is also most unlikely to be clinically significant in terms of HDFN (but I wholeheartedly agree with you that it should be monitored throughout the pregnancy).

I take it that the first pregnancy resulted in a successful delivery of a healthy baby?

Thanks Malcolm.  

I checked it she was not given large dose of anti -D in her first pregnancy.   However in her first pregnancy she developed anti D at 32 weeks where her level was 0.5Iu/ml then at end of her first pregnancy level was 1.0IU/ml. 

1 hour ago, Malcolm Needs said:

I must confess that I am slightly at a loss as to why the 15 week sample could not be used for foetal RHD genotyping, leading to a prediction of the D antigen expression on the foetal red cells, unles

As per routine antenatal sample if booking blood is Rh negative we send sample for FDS for Rh D prediction. 

Could it be because lady had Allo antiD? When lady has Allo anti D do they use different techniques? 

 

 

2 hours ago, Malcolm Needs said:

take it that the first pregnancy resulted in a successful delivery of a healthy baby?

Yes.  

Another thought do you think in 1st pregnancy anti-D could be in IgM nature and therefore level might  be slightly raised? 

 

35 minutes ago, gagpinks said:

Could it be because lady had Allo antiD? When lady has Allo anti D do they use different techniques? 

 

 

Not as far as I know, but I will check for you (but, apologies, it will have to be tomorrow now).

Edited November 22, 20231 yr by Malcolm Needs

25 minutes ago, gagpinks said:

Yes.  

Another thought do you think in 1st pregnancy anti-D could be in IgM nature and therefore level might  be slightly raised? 

 

Thanks.

No, that shouldn't make any difference.

frm5197-41-fetal-rhd-screen-request-form-printable-version.pdf

Why does this form says ( top of the form)  if patients has Allo antiD sample will be rejected for Fetal RhD screening.  So I am sure they will be using different technologies 

The simple answer is gagpinks, but this is the answer I have just received from my friend at the IBGRL (who shall remain anonymous for now).

The question I put was as follows:

"Sorry to bother you yet again, but I have had a query from a friend. I think I know the answer, but I wanted to check with an expert. If a pregnant lady has an allo-anti-D, can this affect cffDNA harvesting from the mother's circulation? I don't think it does unless the anti-D knocks out all of the foetal red cells. Best wishes from this bloody nuisance, Malcolm"

Answer below.

"Hi, that's right, anti-D makes no difference to the cffDNA test. The two biggest problems are false negatives due to insufficient RHD gene in the test sample and mums with a RHD gene (despite pheno typing as D-) leading to strong positive results. Take it easy."

As I said, the friend will remain anonymous for now, but, suffice it to say, he/she is one of the people who do the test, so I think the answer can be trusted!