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Blood groups are determined by specific antigens found on the surface of red blood cells. The ABO system classifies blood into four main groups: A, B, AB and O. Each group can also be either Rh-positive or Rh-negative, depending on the presence of the Rh factor.

Having the same blood group does not automatically create any pregnancy-related complications. Even couples with different blood groups can have healthy children. However, certain blood group incompatibilities, particularly involving the Rh factor, may create health risks for an unborn baby if they are not identified and managed properly.

One important concern is Rh incompatibility. This condition can occur when a mother has Rh-negative blood and her baby has Rh-positive blood. The baby may inherit the Rh-positive factor from the father, even if the mother is Rh-negative.

During pregnancy or childbirth, some of the baby's red blood cells may enter the mother's bloodstream. Her immune system may recognise these cells as foreign and begin producing antibodies against them. This process is known as Rh sensitisation.

These antibodies can cross the placenta during a subsequent pregnancy and attack the red blood cells of an Rh-positive baby. As a result, the baby may develop anaemia, jaundice and other complications. In severe cases, the condition can cause excessive fluid accumulation in the baby's body, known as hydrops fetalis.

The risk is generally associated with an Rh-negative mother carrying an Rh-positive baby, not simply with the husband and wife having different blood groups. An Rh-positive mother does not develop this particular Rh incompatibility with an Rh-negative father.

How Different Blood Group Combinations Affect Pregnancy

The possible outcomes depend on the parents' Rh status and the baby's inherited blood group.

1. Both husband and wife are Rh-positive: There is generally no risk of Rh incompatibility. However, their baby may inherit either Rh-positive or Rh-negative blood, depending on their genes.

2. Husband is Rh-negative and wife is Rh-positive: The baby may be either Rh-positive or Rh-negative. This combination does not create the usual Rh incompatibility risk.

3. Both husband and wife are Rh-negative: Their baby will generally be Rh-negative, so Rh incompatibility is not expected.

4. Husband is Rh-positive and wife is Rh-negative: The baby may be Rh-positive or Rh-negative. If the baby is Rh-positive, the mother may develop antibodies against the baby's red blood cells. These antibodies can affect a subsequent Rh-positive pregnancy if preventive treatment is not given.

Apart from Rh incompatibility, ABO blood group differences between a mother and her baby may sometimes contribute to newborn jaundice. However, most cases do not lead to severe complications.

What Tests and Preventive Measures Are Needed?

Doctors recommend checking a woman's blood group and Rh status during early pregnancy. If the mother is Rh-negative, her partner's Rh status and the mother's antibody screening may also help assess the risk.

If an Rh-negative mother has not developed Rh antibodies, doctors may recommend an injection called Rh immunoglobulin (Anti-D). It is commonly given around the 28th week of pregnancy and again within 72 hours after delivery if the newborn is Rh-positive.

If the mother has already developed Rh antibodies, Anti-D cannot reverse sensitisation. Instead, the pregnancy requires specialist monitoring and appropriate medical care.

Therefore, couples should not worry simply because their blood groups are the same or different. Early testing, regular antenatal check-ups and proper medical guidance are the most important steps to protect both mother and baby.