Pregnancy Testing: Rh Factor And Antibody Screen

Illustration of Rh-conflict in a pregnant mother

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There are a few factors that you must be aware of when you are pregnant, especially the ones you are passing on to your baby. Not just your blood group, your baby also inherits a property known as Rhesus factor (or Rh factor) that is closely linked to their health. To determine if your child is Rh positive or negative, you need to know a few basics first.





What is Rh Factor in blood?

Modern vector line icon of rhesus factor

An inherited protein that is found on the surface of RBC (Red Blood Cells) is called Rh or Rhesus factor. Commonly speaking, you are Rh positive if this protein is present in your blood and Rh negative if it isn’t. It is necessary to know one’s Rh factor in case of medical emergencies for blood transfusion and to avoid complications during childbirth.

To understand Rh factor better you need to also know about antigens. Basically, antigens are substances that when enter your body, stimulate your immune system to produce antibodies that helps fight against infections. The difference between Rh blood group and Rh factor is also worth remembering as the two are often confused as being the same. Rh blood group refers to a set of 50 antigens while the Rh factor is related to the D antigen only, and is responsible for determining whether you are Rh positive or negative.




Rh Positive

If your blood has the Rh factor then you are referred to as Rh positive. 85% of the world’s population is Rh positive, and you can consider yourself to be amongst the majority.

Rh Negative

Having a Rh negative blood group in pregnancy does not affect your health in any way nor does it indicate any kind of illness. The inherited protein Rh is missing from the surface of your red blood corpuscles when you are tested Rh negative.





Rh Status and Pregnancy Complications

Every pregnant woman needs to have her Rh factor tested during the first prenatal visit, and this is usually done by drawing blood samples from a vein in the arm. Rh incompatibility between you and your baby isn’t too much of a concern if you are Rh positive, but if you are a Rh negative mother, there are certain precautions your doctor will recommend during your pregnancy and labour period.

If you are Rh negative and your husband is Rh positive, there is a huge possibility of your baby being Rh positive and your blood type will be incompatible with that of your baby’s. This will not be known till your baby arrives into the world, but it is better to assume so and take precautionary measures accordingly.




Rh-Incompatible

Your body has the tendency to fight against any foreign body that enters your system and to do so they produce antibodies, which are like your little soldiers. If you are a Rh negative mother and are carrying a Rh positive baby, your body is likely to produce proteins known as Rh antibodies when it comes in contact with baby’s blood. This incompatibility does not cause any known concerns during the present Rh negative pregnancy (assuming it is your first) but your next pregnancy could be a concern. Try to take as many positive antibodies pregnancy allows for you to consume. Your doctor will be able to guide you on the same basis of your condition.

Rh Chart of Parent and Baby

To understand the different possibilities of your baby being Rh postive or negative, it is important to analyse your partner’s and your blood and it’s Rh factor type.





Blood compatibility during pregnancy

Mother’s Rh factor Father’s Rh factor Baby’s Rh factor Precautions
Rh positive Rh positive If parents are homozygotes- 100% positive If parents are heterozygotes 50% positive If one parent is a homozygote and the other is a heterozygote- 75% positive None
Rh negative Rh negative The blood of the child in 100% of cases will be RH-negative. None
Rh positive Rh negative If RH positive partner or partner of homozygotes for RH – 50% positive; None
Rh negative Rh positive Equal possibility of being Rh positive or Rh negative Rh immune globulin injections

Source:




Rh Sensitization

Being Rh incompatible may not harm your baby during your current pregnancy (if it is your first one). However, if and when the baby’s blood mixes with yours (a possibility during pregnancy and childbirth), your immune system begins producing antibodies to protect itself against this Rh +ve blood. This is known as Rh sensitization, and if you get pregnant with a Rh positive baby in your subsequent pregnancy, these positive antibodies in pregnancy will attack the baby’s blood.

What if I am Rhesus Negative?

During your first visit to the doctor for your prenatal check up, your Rh factor pregnancy test will be carried out and if you turn out to be Rhesus negative, the baby’s father will be tested to check for results. . If your partner is Rh negative too, your child will be Rh negative (since two negatives cannot create a positive), allowing your body to treat it as its own.





There is a huge possibility that your foetus will carry the Rh positive factor if the baby’s biological father is Rh positive himself. Your baby ( in case of first pregnancy) will face no harm since antibodies to the baby’s Rh factor have not been created by your body yet, but your second pregnancy could turn out to be a high-risk one. A mother’s body creates these antibodies agianst this positive Rhesus factor during the first pregnancy and they remain in her system for a lifetime. If you are Rh negative and are expecting a Rh postive baby during your second pregnancy, these antibodies created by your body will further attack the baby’s RBCs. As a result of this, your baby can become highly anaemic which can also be fatal. The baby can suffer from jaundice, which happens due to the liver’s failure to process the large amount of bilirubin that is produced when the RBCs break down.

How does the Baby’s Blood Mix with the Mother’s Blood?

The mother’s blood does not mix with her baby’s during the course of pregnancy unless a procedure like amniocentesis has been carried out. Other factors like vaginal bleeding, or traumatic events like a car accident , fall or a difficult birth could also cause the baby’s blood to mix with its mother’s. Also, during delivery, there is a possibility of the baby’s blood cells mixing with that of the mother’s.




Blood Test for Rh Status and Antibody Screen

A swab being pressed onto a woman's hand after blood collection

Tests for antibody screening during pregnancy are carried out to determine the presence of certain antibodies in your body. This test is particularly important as these antibodies can attack red blood cells leading to the latter’s deficiency. Following are some blood tests that are recommended by doctors to

Coombs Test (Direct and Indirect)

The Coombs Test (Direct and Indirect) is an effective antibody screening test that can be performed during pregnancy to identify antibodies that attack the red blood cells in the mother’s body.





Direct Coombs Test

This test is effective in identifying the red blood cells that have antibodies attached to them. It is carried out by obtaining a sample of red blood cells from the mother’s body . This test is also done on a new born to find out if the antibodies made by the mother’s body have travelled through the placenta to the baby.




Indirect Coombs Test

This test is carried out by taking a sample of the serum (the liquid part of the blood) and detecting the blood group antibodies in pregnancy that are already present in the blood stream. These are likely to bind with certain blood cells, creating health complications if the blood of the mother and child mixes. This test is also carried out before blood transfusion to gauge the antibodies in a donor/recipient’s blood.


What if my Baby and I Develop Antibodies?

Babies can produce antibodies too, but it is a slow process as their immune systems are not mature and functional till they are about 6-8 months old. They remain susceptible to diseases and illnesses. The immune response, however, is not a sustained one, and the virus or bacteria is not recognised till they are a month old.

Preventing the Development of Antibodies

As mentioned earlier, antibodies are blood proteins that are developed by human body to fight any antigen. These antibodies react chemically with any foreign substances like bacteria and viruses in the blood to fight their presence. They are also known as immunoglobulin.

Rh incompatibility is preventable through the use of special immune globulins, also known as RhoGAM. If the infant’s father is Rh positive or of unconfirmed blood type, the mother is injected with RhoGAM in her second trimester. A second injection is given within a few days of the delivery if the baby is Rh positive.

RhoGAM injections are useful in the prevention of antibody development against Rh-positive blood. Women with Rh negative blood group while pregnant should be injected with RhoGAM after every pregnancy, or a miscarriage or abortion or if the mother has been subjected to amniocentesis.


Rh Incompatibility Treatment

Rh Incompatibility treatment is focused on inhibiting the impact of the incompatibility. The new born is treated in the following ways:

  • Blood transfusions
  • Hydrating fluids
  • Electrolytes to regulate the metabolism
  • Phototherapy (Keeping the baby in proximity of fluorescent lights to prevent excess creation of bilirubin in its blood)

Knowing the Rh factors of the parents helps in foreseeing risks to the health of both the mother and the child. Make sure you are tested as a part of the routine pregnancy tests and let your doctor know if there is such a medical incompatibility between you and your partner.

Also Read:

CBC (Complete Blood Count) Test in Pregnancy
Common Trimester Wise Tests during Pregnancy
Blood Tests in Pregnancy