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It is branch of embryology which deals with causes, mechanism and fetal abnormalities


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TERATOLOGY Professor Muhammad Rafique

Definition :

Definition Teratology is the branch of science that studies the causes, mechanisms, and patterns of abnormal development.

Venerable stage of Embryo :

Venerable stage of Embryo A fundamental concept in teratology is that certain stages of embryonic development are more vulnerable to disruption than others

Incidence :

Incidence It is estimated that 7% to 10% of human anatomic anomalies result from the disruptive actions of drugs, viruses, and other environmental factors. Major structural anomalies, for example, spina bifida cystica , are observed in approximately 3% of newborn infants. Additional anomalies can be detected after birth; thus, the incidence reaches approximately 6% in 2 year olds and 8% in 5 year olds.

Congenital Anatomic Anomalies:

Congenital Anatomic Anomalies The causes of congenital anatomic anomalies or birth defects are often divided into: Genetic factors such as chromosome abnormalities Environmental factors such as drugs and viruses multifactorial inheritance (genetic and environmental factors acting together in a complex manner).

Factors influencing the effect of teratogens:

Factors influencing the effect of teratogens Timing the effect of a teratogen on the developing organism depends on what period in the pregnancy (in development) the child is exposed to the teratogen . Some teratogens cause damage only during specific days or weeks in early pregnancy

Critical Period-:

Critical Period - Teratogens are harmful at any time during the pregnancy-for example, for behavioral teratogens, there is no safe period--- the brain and nervous system can be harmed throughout the pregnancy In prenatal development, the time when a particular organ or other body part is most susceptible to teratogenic damage


Exposure The effect of a teratogen on the developing organism also depends on the dose and/or frequency of exposure of/to the teratogen Threshold effect ---the phenomenon in which a particular teratogen is relatively harmless in small doses but becomes harmful when exposure reaches a certain level (the threshold )

Interaction Effect:

Interaction Effect The phenomenon in which a particular teratogens potential for causing harm increases when it is combined with another teratogen or another risk factor

Genetic Variability:

Genetic Variability Another factor that determines whether a specific teratogen will be harmful is the genetic make-up of the developing organism. Possessing and not possessing certain genes may make the developing child more susceptible to the effect of a teratogen

Examples of Teratogens:

Examples of Teratogens Diseases Maternal Illness 1. Rubella ---a viral disease, if contracted early during pregnancy, can harm the fetus and causes blindness, deafness, and damage to the central nervous system HIVAIDS

Drugs (Medications or Social Drugs):

Drugs (Medications or Social Drugs ) Medicinal drugs ---these are drugs that remedy problems in a person body that in some cases have teratogenic effect Tetracycline, acne medication, aspirin, antacids, diet pills

Psychoactive Drugs:

Psychoactive Drugs Drugs that affect how the mind works i.e , alcohol, tobacco, marijuana, cocaine, heroine and all psychoactive drugs slow down fetal growth and increase the risk of premature labor

Fetal Alcohol Syndrome (FAS):

Fetal Alcohol Syndrome (FAS) A cluster of birth defects, including abnormal facial characteristics, slow physical growth, and retarded mental development and these birth defects are caused by the mother drinking excessive quantities of alcohol when pregnant

Tertogen First Discovered :

Tertogen First Discovered In 1941, the first well-documented cases were reported that an environmental agent ( rubella virus ) could produce severe anatomic anomalies, such as cataracts, cardiac defects, and deafness if the rubella infection was present during the critical period of development of the eyes, heart, and ears.


Thalidomide Thalidomide is an anti-nausea and sedative drug that was introduced in the late 1950s to be used as a sleeping pill, and was quickly discovered to help pregnant women with the effects of morning sickness. It was sold from 1957 until 1962, when it was withdrawn after being found to be a teratogen , which caused many different forms of birth defects phocomelia as a consequence of thalidomide use.

Causes of Spina Bifida :

Causes of Spina Bifida Folic acid Family history Medication valproate carbamazepi Diabetes Obesity

Laboratory Tests:

Laboratory Tests Maternal serum alpha-fetoprotein (MSAFP) test. Ultrasound Amniocentesis

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