[Good practices for the use of biological tools in infectious diseases during pregnancy].

Biological tools are essential in obstetrical infectious diseases for determining immune status, systematic screening, or confirming a primary infection in pregnant women. Early detection of fetal-risk infections, even asymptomatic, is key. Expert centers and multidisciplinary prenatal diagnostic centers are recommended for complex cases.Serological analysis, particularly IgM and IgG testing, is vital for identifying primary infections. Timing and patient history (clinical, vaccination, travel) must be considered. In specific cases, follow-up tests (IgG avidity or PCR) are required for confirmation. Serological testing should be conducted early in pregnancy and within the same laboratory to ensure consistency. IgG avidity tests help differentiate recent from older infections, especially in CMV, rubella, and toxoplasmosis, where gestational timing is critical. Techniques like immunoblot and western blot are used for confirming equivocal or inconsistent serology results.PCR provides highly sensitive detection of infectious agents' DNA or RNA and can be useful before antibodies become detectable. It is particularly useful for diagnosing viral infections from lesion samples, such as HSV or VZV, and plays a key role in prenatal diagnosis on amniotic fluid after maternal infection.