What blood type
rejects pregnancy?

Posted by Dr. Yahya MS on January 15, 2020

Recently I was asked by a patient who had two consecutive pregnancy losses after having normal birth of her first child. She was told that her blood type is the cause of her pregnancy failure. She asked "what blood type rejects pregnancy?"

It is true that some blood types will adversely affect the outcome of pregnancy. But this depend on several other factors apart from the mother’s blood group. Some of these factors include:

  • The type of blood group of the mother
  • The father’s blood group
  • The baby’s blood group
  • The number of pregnancies the woman had
  • The outcome of the previous pregnancy
  • Whether the woman was given Rhogam in her previous pregnancy etc

Blood group types that affect pregnancy

The two major blood group conditions that can potentially affect pregnancy adversely are the ABO and rhesus incompatibility. They account for 98% of baby’s red blood destruction in pregnancy.  They may cause immune‐mediated destruction of fetal red cells that have been ‘sensitized’ by maternal antibodies.

The ABO incompatibility

Although ABO incompatibility occurs in approximately 15 percent of all pregnancies, it results in destruction of baby’s blood cells in only 4 percent of such pregnancies.

The mother has natural antibodies to those blood groups that are different from her own. For example, if the mother is blood group O+, she has antibodies for A, B, AB.

If her baby inherits any of these blood group from his father, those antibodies can cross to the baby and destroy the babies blood cells. This can result in anaemia (decrease blood volume), jaundice (yellowish discoloration of the body) which can affect the baby’s brain. Severe decrease of blood volume in ABO incompatibility is rare and can result in the baby developing heart failure and death may occur.

Destruction of baby’s blood group due to ABO incompatibility can occur in first pregnancy and occurs almost exclusively in mothers with blood group O.

Rhesus incompatibility

Rhesus antigens are proteins on the surface of red blood cells. They are named for the rhesus monkey in which they were first discovered. Individuals that with Red blood cells that have this protein are called Rhesus positive, and those individuals that does not have this protein on the surface of their red blood cells are Rhesus negative. Incompatibility of this type of protein between the mother and the baby is the most common cause of fetal blood cell destruction.

About one woman in seven has a rhesus negative blood group, and if her baby inherited a blood group that is positive from
his father, there is a risk that during pregnancy the baby’s blood cells might stimulate an immune response in the mother’s blood (sensitization).  If this happens and the mother makes
antibodies against the Rhesus positive blood group, there is a risk that her babies could be affected in a future pregnancy. 

Maternal sensitization in a Rhesus-negative mother can be due to a previous exposure to Rh antigen, either through transfusion with Rh-positive red blood cells or pregnancy with a Rhesus positive offspring. Thus, in the absence of transfusion, Rh destruction of baby’s red cell generally does not occur in the first pregnancy.

Rhesus positive male babies are 13 times more likely than their female counterparts to develop heart failure and are 3 times more likely to die from the disease.

Potentially sensitizing events in pregnancy

Any condition that increases the chances of mixing the blood of the mother and that of the baby can make the mother to respond by producing antibodies against the fetal red blood cells. Examples of these conditions include:

  • Miscarriage including thretened miscarriage (bleeding during pregnancy in which the baby is alive and the neck of the womb is closed)
  • Ectopic pregnancy (A condition in which the pregnancy implant outside the womb, with potential to rupture and bleed).
  • Termination of pregnancy, especially when instruments are used
  • Abdominal trauma in pregnancy: such as fall from height, road traffic accidents
  • Bleeding from the womb before childbirth such as when placenta seperates before the baby is delivered, or when the placenta is abnormally situated in the lower part of the womb.
  • When the baby is turn manually from buttock to head presentation (External cephalic version) or any other manipulation of the womb.
  • Childbirth: most of the mixing of mother and baby's blood occur during child birth.
  • When the baby died in the womb, as baby's death can be cause by bleeding or seperation of placenta before the demise.
  • Invavsive procedures during pregnancy such as amniocentesis

Why the first pregnancy is not usually affected?

In rhesus incompatibility, the mother has to be expose to Rhesus positive blood from prior sensitization before she develops
antibodies against the Rhesus positive blood.

The initial response to the fetal blood cells that enter into the mother’s circulation is slow, sometimes taking as long as 6 months to develop. The type of the antibodies produce initially are too large to cross the placenta. These reasons allowed the first baby to not to be affected.

However, in ABO incompatibility, the first baby can be affected. This is because the mother already has antibodies against
the baby’s blood that are naturally occurring in her.

How can the sensitization of Rhesus negative mother be prevented?

Prevention is given to Rhesus negative mother, that does not have antibodies from previous exposure to Rhesus positive
blood. This is done by given Rhogam at 28 weeks of pregnancy and within 72 hours after delivery. It should  also be given when the Rhesus negative mother experience any of the potential sensitizing events in pregnancy.

If for any reason, Rhogam is not given within this period, the patient may still receive the injection as late as 28 days after birth. The longer the injection is delayed the less likely that that
the woman will be protected.

It is estimated that 16% of Rh-negative mothers will become sensitized after their first pregnancy if Rhogam is not given to them.

Women who may avoid the injection

  • Women that already develop antibodies against baby's red blood cells.
  • If the biological father of the baby is known with certainty to be Rhesus negative.
  • If the baby's blood group is known to be negative.
  • Molar pregnancy with confirmed histological diagnosis of complete mole
  • Woman who deliver less than 3 weeks of administration of Rhogam, may not need repeat dose. except if large amount of bleeding occurs.

What happen when Rhesus negative woman already have antibodies in her blood?

When ever antibodies are detected in your blood. The injection isnot benficial. The pregnancy will be closely monitored by your doctor to detect anaemia in the baby using tests, and appropriate intervention will be instituted early.

This post is for educational purpose only. It is not meant to replace your professional medical advice. Please visit your doctor for proper evaluation and management.
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