TERATOLOGY
A 36-year-old woman undergoes a barium enema for rectal bleeding on
February 1, with estimated radiation dose of 4 rad. Her last menstrual
period (LMP) was January 1 and she has 35-day cycles. She was not using
any contraception. On March 15, a urine pregnancy test is positive. She
inquires about the risk to her fetus of teratogenic injury.A teratogen is any agent that disturbs normal fetal development and affects
subsequent function. The nature of the agent, as well as its timing and duration
after conception, is critical. There are critical periods of susceptibility with each
teratogenic agent and with each organ system.
The stages of teratogenesis are as follows:
The types of agents that can result in teratogenesis or adverse outcomes are as
follows:
From conception to end of second week: embryo either survives intact or
dies because the three germ layers have not yet been formed
Postconception weeks 3–8: period of greatest teratogenic risk from formation
of the three germ layers to completion of organogenesis
After week 9 of postconception: teratogenicity is low but adverse effects
may include diminished organ hypertrophy and hyperplasiaInfectious: Agents include bacteria (e.g., chlamydia and gonorrhea cause
neonatal eye and ear infections), viruses (e.g., rubella, cytomegalovirus,