What Are Teratogens?
Teratogens are any agent that disrupts a baby's development when a person is exposed to it during pregnancy. Known teratogens include alcohol, smoking, toxic chemicals, radiation, viruses, some maternal health conditions, and certain prescription drugs. Some teratogens are more concerning than others. How harmful a teratogen is depends on several factors, including the type, amount, duration, and time of exposure as well as genetic influences.1

Type: Some teratogens, including alcohol and smoking, have a more harmful impact on a developing fetus than others.23
Amount: The amount of harm to a fetus increases the more the pregnant person consumes or is exposed to a teratogen.
Duration of exposure: The longer a fetus is exposed to a teratogen, the more dangerous the effects.
Time of exposure: Teratogens are most harmful early in pregnancy, starting about 10 to 14 days after conception to about 8 weeks into pregnancy.
Genetics: Sometimes, the pregnant person's or the baby's unique genetics protect them or make them more vulnerable to certain teratogens.
Why They Are Important
All parents should know what teratogens are and how to avoid them since they can cause harm throughout pregnancy, starting around the time of conception. For instance, the risk of miscarriage is higher when you smoke or drink alcohol or are exposed to radiation and certain toxic chemicals.4 These and other teratogens are also linked to premature birth.

Additionally, 4% to 5% of birth defects are caused by teratogens. These include physical malformations, like spina bifida, cleft palate, or microcephaly (when the brain and skull are underdeveloped), as well as vision and hearing problems. Teratogens can also affect cognitive development. Babies born to a parent who drinks alcohol or has certain health conditions, like thyroid disorders, have been shown to have lower IQ scores.

Source: https://www.verywellfamily.com/that-are-teratogens-2371658
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