A teratogen can be a drug, a chemical substance, an infective agent, a maternal disease or a metabolic alternation during pregnancy that causes a structural or functional anomaly in the embryo or fetus that persists after birth. The importance of teratology, even for clinical medicine, is emphasized by the observation that, notwithstanding the enormous progress made in the last decades in the prevention and prenatal diagnosis of fetal anomalies, congenital defects from environmental causes continue to be a significant public health problem.

To this is added the frequency with which physicians must confront this problem. In Great Britain, for example, it was calculated that about 6 percent of pregnant women use drugs during the first trimester, and that figure rises to 35 percent when the entire pregnancy is considered.

The information sources usually available in the literature are sporadic clinical case reports, which are very useful for generating hypotheses but not for drawing conclusions regarding the relative risks, and case-control studies of the retrospective type. For the latter, data are taken primarily from congenital malformation registries, which are closely linked to clinical teratology services.  Teratology texts and databases that are updated every three months or annually are usually consulted : Micromedex database, Teris and Shepard catalog, Reprotox database  to which  a data bank directly maintained and updated by the counselling service is sometime added.

The primary aim of the teratological counselling service is to provide complete and updated information about the true nature and magnitude of teratogenic risk following a particular exposure.

The second objective of the teratological counselling service is that of monitoring all of the pregnancies exposed to agents that are potentially harmful or for which there is a lack of sufficient information to obtain clinical data in a field. Data about human exposure and pregnancy outcome are, in fact, unanimously considered to be the best information source for risk evaluation and are certainly more useful than data obtained through animal experimentation.

The teratological counselling service is provided by the Genetic Medicine Section of Ferrara University.

The staff consists primarily of physicians and health care workers, assisted by administrative personnel and a computer expert.

Requests for teratological information can be advanced in writing by all those who desire it (physicians, patients), specifying name, surname, pregnancy status (gestational age), type and duration of exposure (physical, chemical, or pharmacological agent including drug dosage). A written response is provided within 48-72 hours (first by fax and successively by mail). A form (for case follow-up), must be filled out and returned (at the end of the pregnancy) by the patient's doctor who contributes in this way to the development of a prospective data bank.