A newly married couple got their daughter quite normal. But the mother was unable to deliver the second child because after conception and before parturition, the embryo got destroyed in the womb. The reason may be that
A. Male and female have \[{\text{R}}{{\text{h}}^ + }\]ve
B. Male has ${\text{R}}{{\text{h}}^ + }$ve and female has ${\text{R}}{{\text{h}}^ - }$ve
C. Male has ${\text{R}}{{\text{h}}^ - }$ve and female ${\text{R}}{{\text{h}}^ + }$ve
D. Both have ${\text{R}}{{\text{h}}^{\text{ - }}}$ve

Hint: This situation of embryo destruction occurs due to the antigen antibody reaction that occurs inside the mother’s body which harms the growing embryo. The blood carries the antigens and when the antigens present in the blood of embryos are not present in the blood of the mother then the antibodies produced in the mothers blood act on the antigen present in the embryo’s blood.

Complete answer:
Our red blood cells have a Rhesus factor which is an inherited protein in the form of antigen. The lack of Rhesus factor makes the blood \[{\text{R}}{{\text{h}}^{\text{ - }}}\] and the presence of Rhesus factor makes it positive${\text{R}}{{\text{h}}^{\text{ + }}}$ . The blood with Rhesus factor is a dominant trait and if found majorly. The blood having no Rhesus factor doesn’t cause any illness but causes problems in the pregnancy. When a female with ${\text{R}}{{\text{h}}^ - }$blood and a male with ${\text{R}}{{\text{h}}^ + }$blood have a baby then the mother can have a normal first pregnancy with a healthy child that has ${\text{R}}{{\text{h}}^{\text{ + }}}$blood which is dominant trait that the child received from his ${\text{R}}{{\text{h}}^{\text{ + }}}$father. But during parturition this blood carrying ${\text{R}}{{\text{h}}^{\text{ + }}}$antigen come in contact with the mother’s blood and the mother’s blood starts making antibodies against it. So when the mother conceives the next time, conception happens but before parturition the antibodies in the mother’s blood destroys the embryo having ${\text{R}}{{\text{h}}^ + }$blood. This happens every time the mother conceives. This condition is known as Erythroblastosis fetalis.

Hence, the correct answer is option (B).

Additional information:
-Erythroblastosis fetalis is a haemolytic anaemia that occurs in a foetus due to trans placental transmission of antibodies from the mother’s blood to the foetal blood.
-When a women having ${\text{R}}{{\text{h}}^{\text{ - }}}$ve blood is impregnated with a man having ${\text{R}}{{\text{h}}^ + }$ve blood then Rho incompatibility occurs. To prevent any problem during second pregnancy the mother is injected with Rho(D) immune globulin at around 28 weeks of pregnancy.
-This haemolysis manifests itself in many ways like if its effects are mild then the embryo will have slight anaemia, in worst cases jaundice occurs due to accumulation of bilirubin which is the product formed after the breakdown of haemoglobin.

Note: Erythroblastosis fetalis is also known as Hemolytic disease of the foetus and newborn (HDFN) or alloimmune HDFN. It can also be prevented by transfusion in which the blood of the ${\text{R}}{{\text{h}}^ + }$ foetus is replaced by ${\text{R}}{{\text{h}}^ - }$blood.