for students

1. Drug use in pregnancy
Introduction
 Significant concern surrounds medication use in pregnancy
 Women take an average of two to three medications per pregnancy and 70%
use medication in the first trimester
 The study of birth defects and their etiology is termed teratology, derived
from the Greek teratos, meaning monster.
 A teratogen may be defined as any agent that acts during embryonic or fetal
development to produce a permanent alteration of form or function
 The incidence of major malformations in the general population is 2% to 3%
The risk of malformation after exposure to a drug must be compared with this
background rate

2. Etiology of birth defects
About 80% of birth defects do not
have an obvious etiology, and of
those with an identified cause,
nearly 95% of cases have
chromosomal or genetic origins
There are undoubtedly
medications that pose significant
risk to the developing embryo or
fetus
Less than 1% of all birth defects
are caused by medications

3. Teratogenicity and developmental period
Exposure must occur during a critical developmental period.
 The preimplantation period is the 2 weeks between fertilization and
implantation and is known as the “all or none” period.
As the zygote undergoes cleavage, an insult damaging a large number of cells typically
causes embryonic death.
 The embryonic period extends from the second through the eighth week
postconception.
It encompasses organogenesis and is thus the most crucial period with regard to
structural malformations.
 The fetal period, which is beyond 8 weeks postconception, is characterized by
continued maturation and functional development.
Functional defects and minor malformations

4. Timing of organogenesis during the embryonic period