<prompt> The consequences of Rh incompatibility are not serious during first pregnancy because:In first pregnancy only IgM antibody is formedAntibody titer is very low during primary immune responseIgG generated is ineffective against fetal red cellsMassive hemolysis is compensated by increased eryth ropoiesis  <response>: As discussed is the preceeding text The initial antibodies which are produced are of IgM variety which cannot cross the placenta and by the time IgG antibodies develop, patient has already delivered. Thus first pregnancy is safe.Another reason isIn sensitised women, anti-D antibodies are produced at such a low level that they are not detected during or after the index pregnancy. Instead, they are identified early in a subsequent pregnancy when rechallenged by another D-positive fetus. 