At your first prenatal visit, we will test your blood for type and factor. Blood types can be O, A, B or AB. The factor can be negative (-) or positive (+).

Women with a negative blood type (“Rh -”) are offered additional testing throughout the pregnancy and after birth, in order to ensure that the baby's blood has not mixed at all with the mom's. Blood mixing could happen as a result of trauma during pregnancy or just as a result of the normal birth process.

The danger of blood mixing is that the mom's body could potentially develop antibodies against the “foreign” blood, prompting an immune response (“sensitisation”) the next time the mom gets pregnant. The blood mixing is only a problem when the baby is a positive blood type. Because this is not known until after birth, all Rh- moms are treated as if they have a positive blood type baby.

In order to find out if there has been any risk to the mom in pregnancy, antibody titers (known as the indirect Coombs' test) are drawn at the beginning of pregnancy and also at 28 weeks. The lab tests will let us know if there is any antibodies in the mom's blood. An indirect Coombs' test may also be done on an Rh- mom if there has been any trauma during her pregnancy, like a miscarriage.

After birth, a Direct Coombs test will be done on the baby's blood, as well as for type and factor. If the baby is indeed a positive blood type, the mom will be offered an injection of Rh(o)Immuno Globulin (trade name Rhogam) within 72 hours of birth. Rhogam may also be offered during pregnancy. This immunization is supposed to protect the mom's immune system, as well as any other future pregnancies.

The decision to accept Rhogam is yours. Here are some ways of minimizing the chances of sensitization during pregnancy:

-a good diet helps strengthen placental bed, making premature separation unlikely.
-citrus fruits daily and 1000 mg C complex/bioflavanoids will help make placent and membranes strong.
-eliminate fluoride (toothpaste, water)- flouride interferes with collagen, which helps attach the placenta to the uterine wall.
-1 g powdered, activated charcoal daily to absorb toxins
-1 tsp magnesium powder in water daily
-kelp, sea vegetables or mineral supplements daily
-fresh garlic
-½ cup elderflower infusion daily

Source:
Anne Frye. Understanding Diagnostic Tests in the Childbearing Year. (120-132)