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
· infertility
· stillbirth
· 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.
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.
Cytomegalovirus (CMV)
Herpes Simplex virus Type I and II
Parvovirus B-19 (Erthema Infectiosum)
Rubella Virus
Syphilis (Treponema pallidum)
Toxoplasmosis
Varicella virus
Venezuelan equine encephalitis virus
Virilizing tumors
Rheumatic disease
Hepatitis B Virus
Human Immunodeficiency Virus
Note: See also Section 13.0