Afetus can be exposed to a variety of harmful agents that may cause birth defects. these agents are referred to as

In  fetus  can  be  exposed  to  a  variety  of  harmful  agent  that  may  cause  birth  defects. These  agent   are   referred  to  as  teratogens
  
    Teratogen  are  agent  or   factor which  causes  malformation   of  the  embryo.  It  cause  abnormalities  in  the   development  of  the  fetus ,  If the  mother  is  exposed  to  it  during  pregnancy. Example  of different  type  teratogen  is   certain  chemical, medication  and  infection.

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