Question

At the time of birth, the presence of which antibody indicates the infection of the fetus (intrauterine infection)
A)IgG
B)IgD
C)IgM
D)IgA

Answer 1

One of the several isotypes of antibodies that are produced by vertebrates. The largest antibody in the group. Also, they are the first antibody to appear in the protection against any initial exposure to an antigen. They were found in B cells having the main function apparently being controlling the activation of B-cell.

Complete answer:
Antibodies are also known as Immunoglobulins (Ig) which are produced in response to antigenic activities.
There are four peptide chains in every antibody, 2, long chains called heavy or H chains, and 2 short chains called light or L chains. Hence, it is possible to represent an antibody ${ H }_{ 2 }{ L }_{ 2 }$. There are several types of antibodies being produced in the body like -IgA, IgM, IgE, IgG
-The infection within the womb is called intrauterine infection. It is usually the infection of the membrane that covers the baby .i.e the umbilical cord and/or the amniotic fluid.
-Intrauterine infection is indicated by an increase in the infant’s serum IgM concentration and is often associated with prolonged unconjugated hyperbilirubinemia and abnormal liver function tests.
The only useful indicator of intrauterine infection before six weeks of age is the estimation of the serum IgM concentration
-Post that, the growth in the IgM concentration may mask any early increase, and specific serological testing might be required to probe.

Additional Information:
-IgM -it is developed during human fetal development at 20 weeks. So, it is the first immunoglobulin to be formed. It doesn’t provide passive immunity to the fetus. It is not able to cross the placenta due to its size. It is the first antibody which responds during infection.

-IgD - are monomeric antibody isotypes found in the plasma membrane of mature B-lymphocytes. It is found in the blood serum in a small amount. Generally, it is made up of two heavy chains of the Delta class and two light chains.

IgA - a very important role is played by this antibody for the function of mucous membranes. The association with the mucosal membrane, the amount of IgA produced is much greater than all other types of antibiotic combined

IgG - the most common antibody present in the blood and other body fluids, helps in protecting against bacterial and viral infections. It also takes time to form after an infection or immunization.
So, the correct answer is,” IgM”.

Note: -The concentration of IgM increased in the infant’s serum which indicates an intrauterine infection. This infection reaches the baby through the mother's blood and across the placenta.
-This interaction is generally caused by rubella, toxoplasmosis, or herpes virus.
-All these infections are proved to be dangerous for a growing fetus.