The following two comments recently appeared on my post addressing Implications of a Negative Blood Type. The first reader's question is worth repeating because MANY readers have asked the same question (in various forms) and the explanation is fairly simple. The second reader's questions revolve around potential complications of Rh-sensitization in someone who is attempting to conceive by in vitro fertilization with donor sperm. Her situation is NOT unique today and many other women may be interested in my responses to her queries as well...
Anonymous said... Hi,I have a daughter who is O negative. I also have a son who is O positive. I am O positive and my wife is O negative. Is this possible?
Kenneth F. Trofatter, Jr., MD, PhD said... To anonymous Sept 24: Yes, it simply means that you are heterozygous for the Rh D antigen. That means you have one chromosome that carries the gene for D and one that does not. Your wife has two that do not because she is Rh-negative and if she had even one dose of D, she would be phenotypically Rh-positive just like you because D is a dominant allele. Anyway, odds are that half of your kids (male and female) would be expected to be Rh-positive and half Rh-negative based on percentages alone (and no other extenuating circumstances). Sounds like that's what's happened so far in your family. Hope that helps. Thanks for reading! Dr T
lotsofdecisions said... Hi. I became sensitized to Rh during my pregnancy with my daughter. My questions:
1) Does the fact that I was sensitized at my daughter's birth impact the problems I may have with a future pregnancy? I'm using donor sperm and know that the donor is O+ and heterozygous. How great is the risk? My titers are around 1:4.
2) After 2 unsuccessful IVFs to avoid having a second O+ child, I am about to admit defeat re: giving my daughter a full sibling. My question: should I consider only O- donors? It seems like using an A- or B- donor could result in as great of issues as if I used my daughter's donor.
3) How concerned should I be about CMV? I'm CMV negative. I've lived in the Northeast as well as the South. It seems like I'd have contracted CMV if I were susceptible to it.
Sorry this is so long. Thanks in advance.
Kenneth F. Trofatter, Jr., MD, PhD said... To lots of decisions Sept 20: 1) Yes, your Rh-isoimmunization could have an impact on a future pregnancy. If your donor is heterozygous for Rh-positivity, there is a 50% chance your babies from that donor will be Rh-positive and potentially at risk for "Rh disease." You are currently at relatively low risk for complications with a titer of only 1:4. The risk begins to rise dramatically once your titer exceeds 1:16. During a pregnancy, I would recommend you have your titer checked every 4-6 weeks, especially if it begins to rise. In fact, if it does rise during a pregnancy, that probably confirms the baby is Rh-positive. We can currently assess risk for fetal anemia by a noninvasive study called Doppler flow velocimetry of the peak systolic velocity in the baby's middle cerebral artery. It's not as hard to do as it is to pronounce!
2) If you are using an Rh-positive donor, you cannot be sure that the baby is not Rh-positive until you test fetal cells by some sort of invasive procedure (chorionic villus sampling, amniocentesis, percutaneous umbilical cord blood sampling). You would be better starting off with an Rh-negative donor because then the baby CANNOT be Rh-positive. It does not matter whether that donor is A-, B-, O-, or AB-. The problem is with Rh, not the major blood group antigens.
3) CMV negativity is a BIG concern to me in your situation. (Check out a couple of my earlier blogs on that subject as well). You may be at risk for contracting that from your donor or you could simply contract it from someone else, especially your daughter, who is VERY likely to pick it up if she spends time around other kids. It is spread by all kinds of body fluids (e.g., blood, urine, and drool) and it is unlikely you are "not susceptible" to catching it; you probably have just been UNLUCKY enough not to have been exposed to it earlier in your life. I say unlucky, because if you did happen to catch it during a pregnancy, the results could be quite devastating to the baby. Thanks for reading and the great questions and BEST of luck to you too! Dr T