Toxoplasma investigation prior to conception

 Following primary testing in the district hospital laboratory, selected specimens are sent to the reference centre for detailed investigation. The results of these investigations place women into one of three categories regarding Toxoplasma status:

1 . Those without detectable specific antibody.

These women have not been infected by Toxoplasma gondii and should be given  appropriate health education to reduce the risk of acquiring infection during a subsequent pregnancy.

2. Those having detectable specific IgG but without IgM.

These women have been infected by Toxoplasma in the past and are now in a state of  chronic, latent infection. Unless there is significant immunosuppression, the patient is not at significant risk of passing the infection to the foetus during a subsequent  pregnancy. Consequently, this group can be reassured.

3. Those having detectable IgG and IgM.

The significance of the presence of IgM depends on the sensitivity of test(s) used. Very  sensitive tests, such as IgM ISAGA, may produce positive results for many months, even years, after onset of infection. Therefore an analysis of all available serological and  clinical information should be made to try accurately determine the onset of infection.

• These women have been recently infected with Toxoplasma and should be counselled as  to an appropriate period to avoid conception. This is usually a minimum of 6 months from the onset of infection but may be longer if the patient has persisting symptoms.

Toxoplasma Serology and Pregnancy

Although toxoplasma infection becomes latent, with cysts persisting in many tissues, including the uterus, these cysts present a very low risk to future pregnancies. Current experience suggests that latent infection is an uncommon cause of abortion, although there is a risk of congenital infection in immunocompromised women. Confirmation of past infection allows for virtually all women the reassurance of immunity and obviates the need for further testing.

In the UK, less than 20% of 20 year old females are likely to be immune to toxoplasma. The percentage with immunity increases slowly in the main childbearing years to approximately 30% at the age of 40. It follows that the majority of women who request a test are likely to be susceptible, in which case they require advice on sources of infection and on precautions for avoiding infection. In some European countries, susceptible women would be retested regularly throughout pregnancy as part of a screening programme to diagnose infection in pregnancy. In the UK there is no formal screening programme, but concerned women should be counselled and in selected cases offered serological testing at booking and, if susceptible, again in the second trimester and at delivery.

A positive Eiken Latex Agglutination does not distinguish between past and current infection. A negative specific IgM test excludes current infection. Even if infection occurs just before conception the risk to the foetus is considered to be small, but women with acute infection are usually advised to wait 6 months before becoming pregnant, and perhaps longer if there are persisting symptoms and signs.