Teratogenesis

Written by docteam Sunday, 28 February 2010 19:02

Teratogenic may be induced at any stage of gestation and may be detected at birth or later. We may define teratogenic as any birth defect. It has been estimated that the average pregnant woman takes about eight drugs during pregnancy. Only 20 % have been prescribed by physician. Because of these , teraogenesis become an increasingly important issue.

Drug Associated with teratogenesis and clinical state
Aminoglycosides : deafness.
Chloroquine : deafness and neurological deficit.
Lithium : possible cardiovascular abnormalities.
Phenytoin : malformation of fingers, cleft palate.
Tetracycline : stained teeth, depressed skeletal growth.
Thalidomide : phocomelia, hearing loss.
Warfarin : hypoplastic nasal structure if  given 10 weeks.

The occurrence of a congenital malformation is dependent on the interplay of the following factors, which are known to influence tetragenicity :

1. Nature of the responsible agent.
2. Accessibility of the agent to the fetus.
3. Duration of exposure to the agent.
4. Stage of fetal gestation.

Prior to implantation- the first 2 weeks following conception the embryo is generally considered to be resistant to environtmental agents other than radiation, possibly because there is no direct circulatory link between the mother and embryo. This interval is form conception to the time of the mother’s first missed menstrual period. The time of organ formation in humans is approximately from 13 to 56 days of gestation : from days 15 to 25 for the nervous system, from days 20 to 40 for the heart, and from days 24 to 48 for the limbs. After the first trimester most organs are formed, although the genital apparatus, teeth, and central nervous system continue to mature. Any malformation will be closely related to the stage of development at the time of exposure to the teratogenic drug or other external agent