A woman with Rhesus negative blood group was advised not to marry a man with Rhesus positive blood group because

Analyze the question: It asks why a Rhesus negative (Rh⁻) woman is advised against marrying a Rhesus positive (Rh⁺) man. This is about Rhesus incompatibility between mother and baby.

Concept:

• Rh⁺ is dominant (the Rh factor/antigen is present on red blood cells). Rh⁻ is recessive (no Rh antigen).
• If an Rh⁻ mother carries an Rh⁺ baby (inherited from an Rh⁺ father), some of the baby's red blood cells can enter the mother's blood, especially at birth.
• The mother's immune system sees the Rh antigen as foreign and makes anti-Rh antibodies.
• In the first pregnancy, the baby is usually unaffected because the antibodies develop late. In later pregnancies, the antibodies cross the placenta and destroy the red blood cells of an Rh⁺ foetus.
• This causes haemolytic disease of the newborn (erythroblastosis fetalis), which leads to severe anaemia, jaundice, brain damage, stillbirth or death of the baby.

Checking the options:

• A. Wrong. The problem is not about transfusing blood from her husband. The issue is the baby's blood.
• B. Correct. Rhesus incompatibility can make the offspring sick and may cause death.
• C. Wrong. Resemblance has nothing to do with blood group.
• D. Wrong. It does not reduce her ability to conceive. The risk is to the foetus or baby, not her fertility.

Answer: B

Exam tip: Remember "Rh⁻ mother + Rh⁺ baby = mother's antibodies attack the baby's blood" (usually from the second pregnancy onward). Whenever you see Rhesus factor with marriage or pregnancy, think of the baby's health, not the mother's fertility.