Rhesus Factor

Rhesus incompatability can affect your subsequent baby.

Each person has a Rhesus factor (Rh) that is either positive or negative. About 85 per cent of the population are Rh positive with the remainder Rh negative.

An incompatibility arises when an Rh negative woman has a partner who is Rh positive, resulting in an Rh positive baby.

If the mother’s and baby’s blood come into contact during childbirth, her body produces antibodies against the baby’s blood.

How is my baby affected?

If you have rhesus incompatibility, your blood is tested every few weeks to check for an immune system response. If you are producing antibodies, the present baby is not affected, but a subsequent pregnancy may be at risk because the mother’s antibodies can cross the placenta and harm the developing foetus by destroying its red blood cells, causing severe anaemia, and possible miscarriage.

Women in this situation are given injections of anti-D, which coats the baby’s Rh positive cells and protects against the manufacture of antibodies.

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