Mother – foetus Rh blood type incapability problems can occur if the mother is ............... and her foetus is...........
- (1)Rh positive; Rh negative
- (2)Rh negative; Rh positive
- (3)Rh negative; Rh negative
- (4)Rh positive; Rh positive
Answer
Why
Correct — option (2), Rh negative; Rh positive.
The stem's "incapability" reads as incompatibility: RPSC's Hindi version of the question prints विसंगति (mismatch), and incompatibility is the word NCERT uses. NCERT's Class 11 Biology chapter Body Fluids and Circulation describes "A special case of Rh incompatibility (mismatching)" between the Rh-ve blood of a pregnant mother and the Rh+ve blood of the foetus.
The mismatch needs both halves. NCERT says an Rh-ve person exposed to Rh+ve blood forms antibodies against the Rh antigen. An Rh-ve mother lacks the antigen; an Rh+ve foetus carries it on its red blood cells.
So the pairing is Rh negative mother; Rh positive foetus.
The idea to remember: the risk arises when an Rh-negative mother carries an Rh-positive foetus.
Why the others are wrong
- (1)Rh positive; Rh negative — This reverses the pairing. NCERT's case of Rh incompatibility is an Rh-ve mother with an Rh+ve foetus.
In NCERT's account the antibodies are made by an Rh-ve person exposed to Rh+ve blood, and they destroy Rh+ve red blood cells. An Rh-ve foetus has no Rh antigen on its cells for such antibodies to attack.
- (3)Rh negative; Rh negative — Here neither blood carries the Rh antigen. The foetus's red blood cells lack the antigen, so its blood cannot trigger anti-Rh antibodies in the mother.
The mismatch NCERT describes needs a foetus with Rh+ve blood, which is what the mother's antibodies act on.
- (4)Rh positive; Rh positive — Here both carry the Rh antigen, so there is no mismatch. The mother's own red blood cells already have the antigen.
NCERT's account starts with an Rh-ve mother forming antibodies against Rh antigens she lacks; an Rh+ve mother does not fit that description.
Concept
NCERT explains that the Rh antigen, similar to one found in Rhesus monkeys, is present on the red blood cells of nearly 80 per cent of humans. People with it are Rh positive; people without it are Rh negative.
An Rh-ve person exposed to Rh+ve blood forms antibodies against the Rh antigen, which is why the Rh group should also be matched before transfusions.
The same reaction can occur across a pregnancy when an Rh-ve mother carries an Rh+ve foetus.
RPSC's 2021 syllabus lists "Food and Nutrition, Blood Groups and Rh Factor." under Science & Technology.
NCERT traces the sequence. In the first pregnancy the two bloods are kept apart by the placenta. During that delivery, small amounts of the foetus's Rh+ve blood may reach the mother, who then starts making anti-Rh antibodies.
In later pregnancies these antibodies can leak into the blood of an Rh+ve foetus and destroy its red blood cells. NCERT calls this erythroblastosis foetalis.
Key facts
- NCERT: Rh incompatibility is observed between the Rh-ve blood of a pregnant mother and the Rh+ve blood of the foetus.
- NCERT: the Rh antigen is present on the red blood cells of nearly 80 per cent of humans (Rh+ve).
- NCERT: in the first pregnancy the foetus's Rh antigens do not reach the mother's Rh-ve blood, because the placenta keeps the two bloods well separated.
- NCERT: in later pregnancies the mother's antibodies can destroy foetal red blood cells, causing severe anaemia and jaundice, or death; this is erythroblastosis foetalis.
- NCERT: it can be avoided by giving anti-Rh antibodies to the mother immediately after the delivery of the first child.
From NCERT Class 11 Biology, Body Fluids and Circulation.
Study next
Common traps
- Order matters: the risky pair is Rh-negative mother with Rh-positive foetus, not the reverse.
- First child versus later children: in NCERT's account the placenta protects the first pregnancy; the mother is exposed during the first delivery, and later Rh+ve foetuses are harmed.
- Prevention is given to the mother, not the baby: NCERT says anti-Rh antibodies are administered to the mother immediately after the first delivery.
A question can give the Rh groups of mother and foetus and ask when incompatibility arises, or ask the name of the resulting condition.
A question can also ask how the condition is prevented, or why NCERT's account spares the first pregnancy.
Related PYQs
The Red Blood cells of a person with Blood group ‘O’ contains Agglutinogen :
- (1) A and B both
- (2) Only B
- (3) Neither A nor B
- (4) Only A
Answer(3)
Same idea of antigens on red blood cells, for the ABO system. That question asks which agglutinogens the red blood cells of a person with blood group O contain (RPSC's key: option (3), Neither A nor B); this one turns on the Rh antigen.
Practice
- practice — not a real PYQ
Erythroblastosis foetalis can be avoided by administering anti-Rh antibodies to –
- (a)the father before conception
- (b)the mother immediately after the delivery of the first child
- (c)the first child immediately after birth
- (d)the mother only after the birth of the second child
Answer(2) — NCERT says the condition can be avoided by administering anti-Rh antibodies to the mother immediately after the delivery of the first child. Options (1) and (3) treat the wrong person, and option (4) comes after the pregnancy it would need to protect. - practice — not a real PYQ
According to NCERT, the Rh antigen is present on the red blood cells of about what share of humans?
- (a)20 per cent
- (b)50 per cent
- (c)80 per cent
- (d)99 per cent
Answer(3) — NCERT says the Rh antigen is observed on the surface of red blood cells of the majority, nearly 80 per cent, of humans. Option (1) is roughly the share without it; options (2) and (4) are not NCERT's figure.