Timeline

Teratogens
Diseases lightwavemedia/Shutterstock	Rubella Rubella (German measles) Effects of exposure on fetus: In embryonic period, causes blindness and deafness; in first and second trimesters, causes brain damage. Preventive measures: Immunization before becoming pregnant.
	Toxoplasmosis Toxoplasmosis Effects of exposure on fetus: Brain damage, loss of vision, intellectual disabilities. Preventive measures: Avoid eating undercooked meat and handling cat feces, garden dirt during pregnancy.
	Measles, chicken pox, influenza Measles, chicken pox, influenza Effects of exposure on fetus: May impair brain functioning. Preventive measures: Immunization of all children and adults.
	Syphilis Syphilis Effects of exposure on fetus: Baby is born with syphilis, which, untreated, leads to brain and bone damage and eventual death. Preventive measures: Early prenatal diagnosis and treatment with antibiotics.
	HIV HIV Effects of exposure on fetus: Baby may catch the virus. Without treatment, illness and death are likely during childhood. Preventive measures: Prenatal drugs and cesarean birth make HIV transmission rare.
	Other STIs, including gonorrhea and chlamydia Other STIs, including gonorrhea and chlamydia Effects of exposure on fetus: Not usually harmful during pregnancy but may cause blindness and infections if transmitted during birth. Preventive measures: Early diagnosis and treatment; if necessary, cesarean section, treatment of newborn.
	Infections, including infections of urinary tract, gums, and teeth Infections, including infections of urinary tract, gums, and teeth Effects of exposure on fetus: May cause premature labor, which increases vulnerability to brain damage. Preventive measures: Good, inexpensive medical care before pregnancy.
Pollutants Gemenacom/Shutterstock	Lead, mercury, PCBs (polychlorinated biphenyls); dioxin; and some pesticides, herbicides, and cleaning compounds Lead, mercury, PCBs (polychlorinated biphenyls); dioxin; and some pesticides, herbicides, and cleaning compounds Effects of exposure on fetus: May cause spontaneous abortion, preterm labor, and brain damage. Preventive measures: May be harmless in small doses, but pregnant women should avoid exposure, such as drinking well water, eating unwashed fruits or vegetables, using chemicals, eating fish from polluted waters.
Radiation Flik47/Shutterstock	Massive or repeated exposure to radiation, as in medical x-rays Massive or repeated exposure to radiation, as in medical X-rays Effects of exposure on fetus: May cause small brains (microcephaly) and intellectual disabilities. Background radiation probably harmless. Preventive measures: Sonograms, not X-rays, during pregnancy. Pregnant women who work directly with radiation need special protection.
Social and Behavioral Factors lzf/Shutterstock	Very high stress Very high stress Effects of exposure on fetus: May cause cleft lip or cleft palate, spontaneous abortion, or preterm labor. Preventive measures: Adequate relaxation, rest, and sleep; reduce intensity of employment, housework and child care.
	Malnutrition Malnutrition Effects of exposure on fetus: When severe, interferes with conception, implantation, normal fetal development. Preventive measures: Eat a balanced diet, normal weight before pregnancy, gain 25–35 lbs (10–15 kg) during pregnancy.
	Excessive, exhausting exercise Excessive, exhausting exercise Effects of exposure on fetus: Can harm fetal growth if it interferes with woman’s sleep, digestion, or nutrition. Preventive measures: Can harm fetal growth if it interferes with woman’s sleep, digestion, or nutrition.
Medicinal Drugs Maxx-Studio/Shutterstock	Lithium Lithium Effects of exposure on fetus: Can cause heart abnormalities. Preventive measures: Avoid all medicines, whether prescription or over-the-counter, during pregnancy unless given by a medical professional who knows recent research on teratogens.
	Tetracycline Tetracycline Effects of exposure on fetus: Can harm teeth. Preventive measures: Avoid all medicines, whether prescription or over-the-counter, during pregnancy unless given by a medical professional who knows recent research on teratogens.
	Retinoic acid Retinoic acid Effects of exposure on fetus: Can cause limb deformities. Preventive measures: Avoid all medicines, whether prescription or over-the-counter, during pregnancy unless given by a medical professional who knows recent research on teratogens.
	Streptomycin Streptomycin Effects of exposure on fetus: Can cause deafness Preventive measures: Avoid all medicines, whether prescription or over-the-counter, during pregnancy unless given by a medical professional who knows recent research on teratogens.
	ACE inhibitors ACE inhibitors Effects of exposure on fetus: Can harm digestive organs. Preventive measures: Avoid all medicines, whether prescription or over-the-counter, during pregnancy unless given by a medical professional who knows recent research on teratogens.
	Phenobarbital Phenobarbital Effects of exposure on fetus: Can affect brain development. Preventive measures: Avoid all medicines, whether prescription or over-the-counter, during pregnancy unless given by a medical professional who knows recent research on teratogens.
	Thalidomide Thalidomide Effects of exposure on fetus: Can stop ear and limb formation. Preventive measures: Avoid all medicines, whether prescription or over-the-counter, during pregnancy unless given by a medical professional who knows recent research on teratogens.
Psychoactive Drugs Shutterstock	Caffeine Caffeine Effects of exposure on fetus: Normal, modest use poses no problem. Preventive measures: Avoid excessive use. (Note that coffee, tea, cola drinks, chocolate all contain caffeine.)
	Alcohol Alcohol Effects of exposure on fetus: May cause fetal alcohol syndrome (FAS) or fetal alcohol effects (FAE). Preventive measures: Stop or severely limit alcohol consumption; especially dangerous are three or more drinks a day or four or more drinks on one occasion.
	Tobacco Tobacco Effects of exposure on fetus: Reduces birthweight, increases risk of malformations of limbs and urinary tract, and may affect the baby’s lungs. Preventive measures: Ideally, stop smoking before pregnancy. Stopping during pregnancy also beneficial.
	Marijuana Marijuana Effects of exposure on fetus: Heavy exposure affects central nervous system; when smoked, may hinder fetal growth. Preventive measures: Avoid or strictly limit marijuana consumption.
	Heroin Heroin Effects of exposure on fetus: Slows fetal growth, increases prematurity. Addicted newborns need treatment to control withdrawal. Preventive measures: Treatment needed before pregnancy but if already pregnant, gradual withdrawal on methadone is better than continued use of heroin.
	Cocaine Cocaine Effects of exposure on fetus: Slows fetal growth, increases prematurity and then learning problems. Preventive measures: Stop before pregnancy; if not, babies need special medical and educational attention in their early years.
	Inhaled solvents (glue or aerosol) Inhaled solvents (glue or aerosol) Effects of exposure on fetus: May cause abnormally small head, crossed eyes, and other indications of brain damage. Preventive measures: Stop before becoming pregnant; damage can occur before a woman knows she is pregnant.

*The field of toxicology advances daily. Research on new substances begins with their effects on nonhuman species, which provides suggestive (though not conclusive) evidence. This activity is a primer; it is no substitute for careful consultation with a knowledgeable professional.