Ionizing radiation and hyperthermia
Ionizing radiation can break chromosomes apart and so alter the DNA structure. This is the reason why unnecessary x-ray examinations during a pregnancy are actively discouraged even though today, thanks to technical advances, the risk of damage to an embryo/fetus by an x-ray examination is estimated to be very small.
It is possible that hyperthermia (from high fever) can have teratogenic effects.
The root cause of the disorder in an infection of the embryo/fetus is a primary infection of the mother. The type and severity of the embryonic/fetal disorder is influenced by the severity and mainly the time of pregnancy in which the infection occurs.
It is primarily virus infections that show a large teratogenic potency. The most well known example for this is the rubella embryopathy. An infection with the rubella virus in the first month of pregnancy leads to abnormalities in roughly 50% of the embryos. The morbidity sinks in the second month of pregnancy to 25% and in the third, to 15%. After infection in the third or fourth month only hearing loss (damage to the inner ear) is observed. In view of the possibility of a rubella infection during pregnancy, young women today are recommended to allow themselves to be immunized against rubella (German measles) when they leave school.
In principle a series of further viral infections during pregnancy can have similar consequences for the embryo/fetus like a rubella infection. The teratogenic potency of most viruses appears to be lower, but this is not known for certain. One does not yet precisely know, for example, the teratogenic potency of a HIV infection, although it is transferred to the still unborn baby.
Besides viral illnesses, other pathogenic agents such as the sporozoon toxoplasma gondii give rise to the feared disease toxoplasmosis by infection during early pregnancy.
Syphilis, which is evoked by the bacteria treponema pallidum, can also have teratogenic effects on the embryo/fetus.
Maternal metabolic diseases
Fundamentally, one distinguishes between pregnancy-specific and pregnancy-unspecific diseases of the mother.
Pregnancy-specific illnesses are frequently summarized under the concept of gestosis. It is therewith emphasized that the pregnancy is the cause of these diseases without going into greater detail concerning the pathogenesis. One distinguishes between early gestosis (occurring during early pregnancy) and late gestosis (in the later stages of pregnancy).
In the pregnancy-unspecific diseases it must be kept in mind that today a coincidence of pregnancy and general diseases is much more frequent than earlier since possibilities for improved therapy of the basic disease not only improve the fertility of the ill woman (e.g., with diabetes mellitus), but also, in almost all cases, permit pregnancies to go full-term.
Malnutrition and starvation of the mother can also lead to damage of the embryo/fetus.