[Exogenous harmful substances in pregnancy and their effects on the embryo and fetus]

Abstract

When using drugs during pregnancy the advantages and risks of a therapy have to be considered carefully. In order to assess the risk of possible teratogenic effects under the influence of external harmful substances the following factors have to be taken into account: the type of the drug administered, kind, dose and duration of the medication, impaired metabolism of drugs owing to diseases of te mother, placenta transfer, time of the exposition during pregnancy, genetic disposition. As in other cases in pharmacology and toxicology there are clear relations of dose and effect as a result of an exposition. High doses, administered for a short time, are extremely dangerous as they may affect the fetus. A deleterious effect on the fetus in the first trimester results in abortions and malformations, in the second and third trimester in general retardations of the fetal development, postnatal impairments of the functional development, increasing perinatal mortality, premature deliveries, stillbirths, transplacental carcinogesis. A long-term exposition or the administration of high doses of different substances at the end of pregnancy may produce syndromes which may possibly endanger the newborn. Following drugs are among these pharmacons: Benzodiazepines, Neuroleptics, tricyclic antidepressants, Lithium, Beta-receptor-blocking agents, Beta-sympathomimetics using as tocolytics, Captopril. Withdrawal syndromes of the newborns have been described after a long-term therapy with certain drugs or due to drug addiction of the mother. In every pregnancy there is a certain risk of giving birth to an abnormal child. Malformations observed at birth or immediately afterwards happen according to the definition with a frequency of 2 to 4% (FRG), according to sources from other countries with a frequency of 2.5 to 6.5%. If you add anomalies diagnosed within first year of life a deformity rate of 10% can be worked out, approximately 4 to 5% of which can be traced back to the exposition to drugs and environmental chemicals. A teratogenic influence would always have to work together with other factors to cause a faulty development of the fetus.