Diagnosis of Toxoplasmosis organisms in pregnancy period. The ever existing dilemma.

Diagnosis of Active Toxoplasmosis in Pregnancy:-A ever existing dilemma:-Obstetricians are often confused once IgG titer is high & raised IgM-more so if there is demonstrable foetal anomaly Sonologically at a later date:--It is difficult to confer some abnormalities of foetus, God forbid if appear later in this case, that whether such abnormalities (if at all appear in this case) - were due either to CMV or to Rubella with certainty: There may be other causes of CM of foetus.

Reasons are:--Firstly, in our country CMV IgG antibodies are as high in 95% +ve of all women of child bearing age. Though presence of IgG antibody do not guarantee against re-infection. Secondly :-One cant equate cong malformations due to  re-infection as re-infection rate is quite high in our country and in such cases a low IgM antibodies have less predictive value( in re-infection cases-I mean).What, then  is solution? Therefore, molecular methods of diagnosis are more relevant.

Please do not equate presence of  IgM means acute maternal / foetal infection:- Mere presence of high titers of IgG Rubella /IgG CMV in pregnancy do not always mean that the  concerned foetal abnormities were due to acute  viral infection acquired in the pregnancy. At best one can suspect acute viral infection, if IgM is very high. Because in most cases prepregnancy serological status remain unknown to us. Such high titers of antibody might have present earlier i.e. prior to pregnancy. Only an avidity case can prove whether the viral infection was recent or not.

What is meant by avidity test of antibodies? The terms avidity or “functional affinity” imply to quantify the net antigen –binding force/ capability of population of antibodies. IgG antibody affinity is now commonly done in many centres if India nowadays. This will diagnose the and differentiate between reactivation, re-infection, or primary infection. The high avidity rules out recent infection of less than 4 months even if IgM abs is present.  Therefore low avidity is not an absolute indication of recent infection. High avidity with 10% positive predictive value to rule out acute infection.