The risk of foetal infection is most common when the mother acquires a T. gondii infection after conception and very rarely when infection occurs within a few weeks before. Where the mother becomes infected during the first trimester of pregnancy, the risk of maternal/foetal transmission is reported to be about 15 - 25% including treated and untreated cases. The risk of transmission is higher where infection is acquired later in pregnancy. Conversely the subsequent risk of foetal damage, including death, is highest when transmission does occur in the first trimester and is progressively less when it occurs in the second or third trimesters.

• The absence of a significant rise in antibody titres between the samples taken at 13 and 16 weeks of pregnancy, together with no detectable IgM, excludes an infection acquired within the 6 months prior to the first sample, and hence toxoplasmosis is unlikely to be the cause of intra-uterine death. IgG avidity and the detection of specific IgA and IgE are also appropriate tests for estimating the duration of infection.
•  Latent Toxoplasma infection is a possible but uncommon cause of recurrent spontaneous abortions.

Intra-uterine death in the immunocompetent

The incidence of intrauterine deaths as a result of toxoplasmosis is not established, however, there are a number of reports in the literature that have suggested single or recurrent intra-uterine deaths to be the result of a Toxoplasma infection acquired by the mother many months or years prior to conception. However evidence to support this is mostly indirect and so the present generally held view is that such events, if they do occur, are rare.

Intra-uterine death in the immunodeficient

In the immunodeficient, reactivation of latent tissue cysts resulting in parasitaemia, with or without clinical symptoms, is common. In the immunodeficient pregnant woman with latent infection, the risk of reactivation resulting in infection of the placenta and hence risk to the foetus is unknown. Specific prophylaxis should be considered in such cases.