An O positive offspring of two O negative parents?

November 20, 2007 6:15 AM

Can two parents who are both O negative have an O positive offspring?

A while back I was discussing anti-D injections with my midwife. She told me that even though both my baby’s father and I have O negative blood groups, I should still be given the injection because there’s a small chance the littl’un would have O positive blood.

Can this be possible, even though O negative genes are recessive? (Or was the midwife just giving me a story to tell the hubbie in case I’ve been cheatin’ around?)

posted by low_horrible_immoral to health & fitness (9 comments total)

it's a typical cover-your-ass move by a midwife or ob/gyn to give Rh immune globulin injections to any Rh negative woman even if the father is Rh negative. Yes, it is to cover you in case your partner isn't the father - but could also be to cover you in the rare case that his blood test was inaccurate.
posted by tuff at 6:35 AM on November 20, 2007

Some individuals have red blood cells which are D_el, meaning they have a very low level of D antigen (the molecule on the surface of red blood cells that makes them Rh-positive) which is generally not detectable by Rh factor testing, but can induce anti-D antibodies in a true Rh-negative individual. If the baby's father was D_el, he would type as Rh-negative but in fact be Rh-positive (with much much lower levels of the antigen than most Rh-positive individuals), and the baby could also be D_el which would potentially still result in the usual complications with an Rh- mother carrying an Rh+ child.

Source (pp. 155-163)
posted by DevilsAdvocate at 6:56 AM on November 20, 2007

Nice answer, DevilsAdvocate; there's a nice review that talks about this a bit more, but all that being said, I haven't seen any clinical recommendations at all that advise to give Rhogam to a mother of a fetus with two known Rh-negative parents.
posted by delfuego at 7:25 AM on November 20, 2007

And, just to be pragmatic here, a good midwife would know that studies have shown up to 30% of children born are not fathered by the husband/boyfriend. It would seem to be practice to give anti-D to all Rh- mothers.
posted by OlderThanTOS at 7:43 AM on November 20, 2007 [1 favorite has favorites]

We shotgun every pregnant female who is Rh negative with RhoGam (although we currently use WinRho now).

And DevilsAdvocate is correct except in the blood-banking world is commonly referred to as 'Weak D.' It may help you google.
posted by i_am_a_Jedi at 8:23 AM on November 20, 2007

Thanks for the Source, DevilsAdvocate.
I've been spending too much time in Rh haplotypes lately and had not heard of D_el. I though you were talking about D^u (i_am_a_Jedi's "weak D"), but this article seems to say it's a different antigen.

I've been working with a company that makes blood testing kits and they don't test for D_el. The Red Cross document says it's only detectable by elution testing. D_el can be detected with antisera.
posted by MtDewd at 8:38 AM on November 20, 2007

I haven't seen any clinical recommendations at all that advise to give Rhogam to a mother of a fetus with two known Rh-negative parents.

That’s the one-size-fits-all NHS for you.

That is just the answer I wanted, thank you, DevilsAdvocate. Luckily I don’t think I need it to placate a cuckolded hubby, but you never know! My midwife is v. practically and pragmatic – but she also insisted that medically speaking, it was possible.
posted by low_horrible_immoral at 9:07 AM on November 20, 2007

That’s the one-size-fits-all NHS for you.

Nope, to be clear, I'm a board-certified (pediatric) hematologist in the US, and know the Rh-alloimmunization guidelines pretty well; ACOG's current practice bulletin still doesn't make the recommendation for RhoGAM/WinRho to Rh-negative mothers when the father is "known to be Rh-negative".
posted by delfuego at 2:16 PM on November 20, 2007

It's hardly a case of one-size-fits-all. The rate of "undetected" illegitimacy (by the not-father at least) is around 1 in 10 in the UK. It's more a case of one-size-fits-1-of-10-so-well-that-the-other-9-just-have-to-have-their-injection-and-like-it.
posted by roofus at 6:17 AM on November 21, 2007