When the mother and baby have different blood groups

Women with a less common Rh-negative blood group are monitored extra carefully during pregnancy. If the foetus has Rh-positive blood , the mother risks developing antibodies against the baby's blood. This known as Rhesus isoimmunisation.

If the antibodies enter the baby's blood while it is in the womb, the baby may develop anaemia. The Rhesus isoimmunisation can become more severe with each subsequent pregnancy. Further reading: Newborn screening and newborn exams  and Pregnancy pains and discomforts – a complete list

There are various effective ways to monitor and treat mothers and babies with Rh incompatibility. Because Rh-negative mothers are so carefully monitored these days, this unusual pregnancy complication has almost completely disappeared.

Different blood groups
Human blood is classified in different groups. The most well-known blood group classification system is the AB0 system with or without the Rhesus factor (Rh).

If you don't have the Rhesus factor in your blood, you are Rh negative. If an Rh negative woman conceives a child with an Rh positive man, the child may inherit the Rhesus factor from the father. If this happens and the mother's blood mixes with the baby's, which often happens during delivery, her body may start producing antibodies against this alien factor.

The woman's blood group is determined at the start of pregnancy
When you register at the maternity clinic at the start of your pregnancy, the midwife takes a blood sample. The result shows your blood group and whether you are Rh negative or Rh positive.

In some places in Sweden, the midwife also checks the baby's blood group during this test. This practice is being introduced in more places. If you have Rh negative blood without antibodies and are expecting an Rh positive baby, you will be injected with Anti-D immunoglobulin in week 28 of gestation. This prevents you from developing antibodies against the Rh factor in the baby's blood (Rhesus isoimmunisation).

Protection for future pregnancies
In subsequent pregnancies, these antibodies enter the baby's blood through the placenta. If the subsequent baby is also Rh-positive, the antibodies attack its blood, causing the baby to become severely ill.

These days, all Rh negative mothers who have given birth to an Rh positive baby are injected with Anti-D immunoglobulin, a type of vaccine that prevents Rhesus isoimmunisation in the event of a subsequent pregnancy. The injection is administered within 72 hours after delivery.

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