Introduction

With the term "embryopathies" one is speaking about congenital abnormalities that appear during the embryonic period.
Before the 14th day an insult (injury) to the embryo will not cause an abnormality because the embryo either repairs the damage or dies (spontaneous miscarriage).

On the other hand, in the course of the embryonic period, during which numerous mitotic divisions and organogenesis occur, the embryo is very vulnerable and most congenital abnormalities happen then.

Fetopathies are the abnormalities that occur after the 8th week and up to delivery. The sensibility to injurious substances (noxae) is clearly reduced in the last two trimesters of pregnancy.
Most of the organs already exist by this time and are thus less susceptible. One exception is the cerebral cortex which, between the 8th and 15th weeks, is especially sensitive to noxae.

Classification of the congenital abnormalities

One designates as congenital abnormalities all those that appear due to an interruption or deviation of the normal development and thus lead to changes in form and structure. In this designation the cause is ignored.
These abnormalities are irreversible. In the following section some definitions are given.

Some important definitions

• Primary abnormality:
  Defect (genetic anomaly) in the structure of an organ or a part of an organ that can be traced back to an anomaly in its development (spina bifida, cleft lip, congenital heart defect).
  
  
• Secondary abnormality ("disruption"):
  Interruption of the normal development of an organ that can be traced back to outer influences. Either teratogenic agents (infection, chemical substance, ionizing radiation) or a trauma (amniotic bands, which led to an amputation) are involved.
  The most widespread infectious agents are the rubella virus, the cytomegaly virus and the toxoplasmosis parasite (toxoplasma gondii). To the chemical, teratogenic agents belong thalidomide, warfarin, chloroquine (malaria medicine) and lithium.
  It is important to understand that a congenital abnormality is not necessarily inherited.
  
  
• Deformation:
  Anomalies that occur due to outer mechanical effects on existing normal organs or structures.
  
  
• Dysplasia:
  Abnormal organization of the cells in a tissue (e.g., osteogenesis imperfecta). Numerous dysplasias are genetically caused (e.g., achondroplasia).
  
  
• Agenesia:
  The absence of an organ due to a development that failed to happen during the embryonic period.
  
  
• Sequence:
  When one, single factor results in numerous secondary effects, leading to several anomalies, one speaks of a sequence (e.g., Potter's sequence: not enough amniotic fluid because urine was not produced in large enough quantities. This leads to an oligoamnios. The fetus is crushed, the face is contused, the hips are shifted, and the lungs are smaller than normal [hypoplasia]).
  
  
• Syndrome:
  A syndrome comprises a group of anomalies that can be traced to a common origin (Down syndrome occurs due to a trisomia of the 21rst chromosome and leads to a number of characteristic anomalies).