nbme sec3 form1 query - suchetakrishna

[ArchivalUser]

plz somebody explain this
A 25 yr old woman gravida1 parity0 who is Rh negative delivers a full term Rh positive neonate.The mother is given prophylactic antiD Ig immediately postpartum. During her second pregnancy 3 years later she is screened each trimester for Rh(D) Abs.An indirect antiglobulin test done during the 3rd trimester indicates the presence of anti Rh (D) antibodies in her serum.Which of the following is the most likely mechanism for the occurence of these maternal Abs.

a)Anamnestic production of maternal antiRh(D) immunoglobulin

b)Intrauterine transplacental fetal-maternal haemorrhages during the second pregnancy

c)Residual circulating prophylactic anti-Rh(D) Ig

d)Transplacental passage of fetal IgG anti-Rh(D)Abs

Ans is (B) but how is it so when she was immediately Anti(D) Ig immediately after the birth of her first child

[ArchivalUser]

there are 2 clues in the question
1.her second pregnancy is 3 years later: where as anti D Ig lasts for 3 months only.. so it cant be the only that she recieved 3 yrs back
2.she is screened each trimester for Rh(D) Abs.An indirect antiglobulin test done during the 3rd trimester indicates the presence of anti Rh (D) antibodies in her serum: Now she tested +ve in only 3rd semester thats when highest chance is present for fetal-maternal haemorrhages as cytotrophoblast is absent then.

hope it helped

[ArchivalUser]

Thanks a lot.It really helped.
Sucheta