16.1  Introduction

16.2  Teratogen

16.3  Exposure Hazards

16.4  Known Human Teratogens

16.1       Introduction

Reproductive hazards may cause alterations in the genetic make-up of a cell, response to hormones, or metabolic pathways.  Such hazards may affect both male and female reproductive systems. A reproductive hazard may:

         inhibit implantation of a fertilized egg

         block fertilization

         cause death or abnormal development of an embryo

The resultant effect of the above may be:

         spontaneous abortion



         malformed offspring


16.2       Teratogen

A teratogen is an agent that causes congenitally malformed offspring.  It may affect the mother directly through interference of transplacental exchange of nutrients, or by actually crossing the placental barrier and directly affecting the developing fetus.  Teratogenic effects are normally not hereditary, but may result from mutagenic damage to germ cells or embryonic cells, or may involve other toxic effects.  They cause permanent alterations in the form or function of offspring by acting at specific times during development; timing is as critical as exposure, during certain periods, and results in specific adverse effects.  For example, during the 3rd to 8th week of pregnancy, the organs are developing, and the placenta, which acts as a barrier to many toxicants, is not completely formed until the 8th or 9th week.


16.3       Exposure Hazards

Female             Females have a lifetime supply of eggs at birth, so any mutations to these eggs will be permanent.  Furthermore, agents acting upon the female fetus at the time of egg formation could change the genetic structure of the fetus' ova before birth.  Exposures during the first trimester represent the greatest risk. 

Male                Male germ cells are continually replenished, making damage to sperm cells temporary, affecting only those present at the time of exposure or damage.  Still, exposure to agents may result in mutations in sperm that are transmittable to offspring.  Miscarriages and birth defects may also be attributable to male exposure to agents.


16.4       Known Human Teratogens

Cytomegalovirus (CMV)

Herpes Simplex virus Type I and II

Parvovirus B-19 (Erthema Infectiosum)

Rubella Virus

Syphilis (Treponema pallidum)


Varicella virus

Venezuelan equine encephalitis virus

Virilizing tumors

Rheumatic disease

Hepatitis B Virus

Human Immunodeficiency Virus


        Note: See also Section 13.0