A lot of drugs have side effects or undesired actions beside its therapeutic effect. Teratogenic drugs are those which exploit the fetus and definitely should be avoided in pregnancy.
below down the most common teratogenic drugs and their effects:
phocomelia and multiple defects
cleft palate, hydrocephalus, multiple defects and foetal death
virilization; limb, esophageal, cardiac defects
virilization of female foetus
vaginal carcinoma in teenage female offspring
Tetracyclines & Glycylcyclines
discolored and deformed teeth, retarded bone growth
depressed nose; eye and hand defects, growth retardation
hypoplastic phalanges, cleft lip/palate, microcephaly
neural tube defects, other abnormalities
spina bifida and other neural tube defects
low IQ baby, growth retardation, fetal alcohol syndrome
hypoplasia of organs, growth retardation, fetal loss
fetal goiter, cardiac and other abnormalities
premature closure of ductus arteriosus
craniofacial, heart and CNS defects
Once you become pregnant, or even when you plan for pregnancy you have to consult a pharmacist or physician about every single medication and read the insert leaflet carefully to avoid any harm to you or your fetus.
FDA has a specific classification for drug labeling during pregnancy:
This is a good website to check any medication for your baby safety: http://www.safefetus.com/
Again and Again, you have to consult a health care professional with your case before using any medication whatever it is during your pregnancy.