Noami Starsiak

I love old black and white movies, where dapper men and quick witted women fall in love while exchanging snappy dialogue. When these movies end in a wedding there is always a line put in about the happy couple having to go get a blood test first.While the pre-wedding blood test isn’t a requirement for marriage now days, it did give couples some useful information like blood type. Anyone who took high school biology might remember that blood is grouped as A, B, and O with either a + or – after. This positive or negative refers to Rhesus factor antigen which can induce an immune response (kind of like pollen in spring). In every day life this has almost no impact but, when you try to make a baby, Rh factor can make things tricky.

If you’re a woman who has a positive blood type there isn’t really isn’t anything to worry about, your body is already used to having Rh antigens. But if you’re a woman with a negative blood type things can get complicated and it centers about the blood type of the dad. If the baby’s father also has a negative blood type then you’re okay. If the baby’s father has a positive blood type then there’s a chance of the baby also inheriting that Rh antigen.

Remember that an antigen causes an immune response? Well, for an Rh- mom who has an Rh+ baby there is a chance that if the bloods mix then mom’s body might think the baby is an invader (like allergy season times 1,000). Now the chance is small, because the placenta is amazing at keeping the two blood supplies separate, but if a pregnant woman has a fall or some other impact to her stomach it can cause mixing. There is also some mixing that occurs during birth, which means the risk of an immune response goes up with each baby.

However, there are measures that can help to lower the risk. Rhogam is a shot that is given at 28 weeks into the pregnancy and again after birth to lower the chance of sensitization, and is accepted as the general standard of care. If you have concerns about the ingredient in your medications there is also WinRho SD available, which does not contain thimerosal. So while the required blood test is a thing of the past, knowing some basic info about you and your partner can prepare you for questions that might come up later on.

Naomi Starsiak is a birth and postpartum doula, a placenta encapsulation, a natural birth consultant, and the co-owner of A Peaceful Birth doula & childbirth service. You can find her on Facebook at Have a question? E-mail it to Naomi at

Lockwood Law


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