The fetal-placental barrier protects the fetus, as a bulwark, against most attacks but not against toxic products as alcohol ,tobacco (which are the subject of a specific article on this site) or drugs. Moreover some highly infectious pathogens such as rubella, toxoplasmosis, influenza or cytomegalovirus can contaminate the fetus.
That is why it is recommanded, before to schedule a pregnancy, to have a clear information of your serological status to some of these pathogens. A list of the serological tests to be performed may be prescribed by your GP or gynecologist, according to the contents of your medical record.
Serological status for rubella and toxoplasmosis are routinely requested.
Such assessments consist to quantify, from a blood sample, the level of antibodies (immunoglobulins) specific for the disease.
Two types of immunoglobulin can be researched:

- Immunoglobulins IgM, which reveal a recent contamination.

- Immunoglobulins IgG, which, when detected alone (without the corresponding IgM), indicate an acquired immunity as a result of an old infection - It means that the subject is immunised against the disease and is able to protect the fetus during pregnancy.

The kinetics of appearance of antibodies may vary depending on the infectious agent.

If such diseases are generaly not severe in adults, they sometimes be unnoticed, they are very dangerous for the fetus at certain stages of its developpement if contracted by non immunised pregnant.

With regard to rubella, an effective vaccine exists.
For toxoplasmosis, if the future mother is not immune, a regular monitoring of the specific IgM will be necessary during the pregnancy, in order to start a treatment in case of an outbreak of this disease.