Prenatal antibody test in pregnancy
When you are pregnant, one of
the prenatal tests you may have is an antibody test or antibody screening. It
looks for certain antibodies, special proteins made by your immune system, in
your blood.
You may have these antibodies
if you have received blood from a donor or have had a baby before. It's also
possible that your body produces it when your blood types and your baby's don't
match.
Some of these antibodies can
pass from you into your baby's bloodstream, where they can cause harm. Antibody
tests let you and your doctor know if you have them so you can take steps to
protect your growing baby.
Why are you being tested
Your immune system produces
antibodies to fight what it thinks is not you. In most cases, this is normal
because antibodies usually target microbes. And when you're pregnant, your
immune system takes care of your baby too. But if your red blood cells are
different from those of your child, this can cause problems.
By far the most common is
related to the + or - part of your blood type, called the Rh factor. Many
people are Rh positive, which means they have the Rh protein in their red blood
cells. Rh negative people do not. Thus, they produce antibodies to attack any
Rh-positive blood cells that enter their body.
If you are Rh negative and
your child is Rh positive, your blood may contain Rh antibodies that can spread
into your child's blood, where they attack and destroy your child's red blood
cells. This can cause a very serious and life-threatening form of anemia.
Your body may have made other
antibodies that can also attack your child's red blood cells.
How it's done
You should have your blood
type checked early in your pregnancy, possibly at your first prenatal visit. If
you are Rh negative, you should have an antibody test during the first 3 months
of pregnancy.
The technician uses a needle
to take a sample of blood from a vein in your arm or forearm. You may feel a
small prick in your skin and some bleeding or bruising where the needle was
inserted.
They will then send the sample
to a lab for an indirect Coombs test, which checks red blood cells for
antibodies.
What the results mean
A negative antibody test tells
you that there are no harmful antibodies in your blood. If you are also Rh
positive, you can safely carry a baby with + or - blood type. Relax and enjoy
your pregnancy!
If the test is negative and
you are Rh negative, you will need another test at about 28 weeks pregnant. If
it tests negative again, your doctor will likely prescribe a drug called
Rho(D)immunoglobulin to stop your immune system from making Rh antibodies.
These antibodies may not cause
problems for your first child, but the vaccine will also help prevent problems
if you become pregnant again.
A positive test means you already have antibodies in your blood. If it's Rh antibodies, the vaccine won't help. Your doctor will monitor you and your child closely. If you have problems during your pregnancy, your baby may need a premature delivery or a blood transfusion through the umbilical cord.