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
