Some environmental factors and some chemical factors faced during pregnancy can cause malfunctions at fetus. The effect of a teratogenic agents on pregnancies shows differences according to the period of pregnancy, the characteristic of agent, the dose and  exposition time.

At the first two weeks of pregnancy, the effect is either losing the baby or having zero-effect at fetus. The effects of these agents are mostly seen between the first 3-10 weeks of pregnancy because of organogenesis. For the later periods of pregnancy there is almost no bad effects of agents at fetus.

In pregnancy periods if a woman id thought to expose an tratogenic agents, The information is evaluated carefully and the family is given genetic consultancy.