Risk assessment of drug use in pregnancy: prevention of birth defects.

Some developmental disorders are preventable by primary prevention, i.e. by avoiding exposure to microorganisms or chemicals that cause developmental disorders. This is not only important for physicians prescribing drugs, midwives monitoring pregnancies, but especially for parents taking the responsibility of having a baby; moreover, this fact is of importance for teratogen information services and public health authorities, both having preventive roles to play. Knowledge of the different pre- and postnatal developmental stages and the reproductive cycle is essential to understand this statement. The basic principle in reproductive toxicology and teratology is that the response of an organism to a teratogen depends upon the nature and the dosage of the substance, the stage of development of the embryo/fetus and its genetic make up. Chemical agents of different nature can induce developmental disorders either via the mother and perhaps via the father. The common consent that the vulnerable stage of development is only the first trimester of pregnancy is not correct. From oogenesis and spermatogenesis to at least the first years of life the developing organism is susceptible to harmful effects of chemical agents, including drugs. Developmental disorders include not only malformations visible at birth, but also spontaneous abortions, fetal death and functional deficits including behavioural defects. Studies both in the human and in laboratory animals make it possible to select substances to avoid exposure to developmental toxicants which are already on the market or still under development. This implicates a multi-step procedure leading from risk-evaluation, risk-assessment, and risk-communication to risk-perception and the according action (risk-management).