2. teratogens.ppt. during pregnancy bscnursing

Teratogen

1. © 2009 The McGraw-Hill Companies, Inc. All rights reserved

Teratogens

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© 2009 The McGraw-Hill Companies, Inc. All rights reserved

Teratogens are defined as agents extrinsic to the embryo
or fetus which can exert a deleterious effect leading to an
increased risk of:

Malformation -physical defect

Carcinogenesis – increased risk of cancer

Mutagenesis – increased risk of genetic disease

Altered function – mental retardation

Deficient growth – IUGR

Pregnancy wastage – abortion & still birth

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© 2009 The McGraw-Hill Companies, Inc. All rights reserved

Teratogens may exert a very mild & transient
effect so that they may not ultimately produce
any recognizable ill effect in exposed
pregnancies or may cause such a profound
effect so as to lead to gross abnormalities

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© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Classification
Teratogens may be classified as:

Drugs & chemicals eg. Thalidomide, lead & mercury

Infectious agents e.g. rubella, cytomegalovirus &
toxoplasma

Radiation e.g. exposure to X ray or radiation

Mechanical compression, deformation & disruption
of fetal development. E.g oligohydramnios

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© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Mechanism

Teratogens exerts their adverse effects in diverse ways:

Interfering with the rate of proliferation of actively growing
tissues (viral infection & ionization) or in its extreme form
causing cell death, so that the available tissue for organ
growth & development is affected

Altered biosynthetic pathways ( chromosomal or genetic
disorders)

Abnormal cellular and tissue interactions at times of critical
development (diabetes)

Extrinsic factors ( tissue compression by amniotic bands,
septum)

Threshold interaction of genes, single or multiple, with
environmental teratogens.

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© 2009 The McGraw-Hill Companies, Inc. All rights reserved
General principles with regards to the mode of teratogens
1. The susceptibility to a teratogen, and the degree of damage
caused by it, depends upon the stage of embryonic development
at which the embryo or fetus is exposed to the teratogen.

When a teratogen acts before differentiation of germ layers, the
effects are drastic and often lead to death of the embryo.

The organ systems of the fetus are established between 3-8
weeks of pregnancy, and this is referred to as the embryonic
period. Most anomalies are produced through the action of
teratogens during this period. Therefore during the fetal period
teratogenic influences become much less severe.

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© 2009 The McGraw-Hill Companies, Inc. All rights reserved
2.The type of malformation produced depends on the exact
timing of the teratogeic influence. Each organ seems to
have a critical period during which it is most sensitive to
teratogens
3.The susceptibility to a teratogen is influenced by genetic
factors. A fetus of one genotype can be much more
susceptible than a fetus of another genotype to the same
teratogen
4.Teratogenic agents act by influencing metabolic processes

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© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Teratogens
Infections :

some disease producing organisms (eg. Virus) or
harmful substances produced by them (toxins) can pass
through the placental barrier and reach the fetus.
Examples are syphilis, chickenpox, measles and
toxoplasmosis

When the mother suffer from German measles in the
early months of pregnancy, the offspring often has
cataract, anomalies of the heart or deafness

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© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Malnutrition:

The developing fetus requires all elements of
nutrition, in adequate quantity, for normal
development

Antigenic reactions:

In case of Rh negative mother has an RH positive
fetus, some Rh –antigen from the fetus can enter
the