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A teratogen is a substance, organism or process that may harm a baby during pregnancy. Teratogens can be diseases, medications, drugs, alcohol or environmental exposures.

 If you are curious or concerned about any of the following information, please contact:

Alcohol related questions
Alcohol and Drug Services at 667-5405 in Whitehorse or 1-855-667-5777, local 5405 in Yukon communities.

Questions regarding other teratogens or teratogens in general
Shannon Ryan at Congenital Anomalies Surveillance Yukon at 667-8563 in Whitehorse, or 1-800-661-0408, ext. 8563 in Yukon communities.

(Health care providers can visit: for more detailed information.)

Many things can influence the effect than an exposure can have. These include the timing of the exposure during pregnancy and the dose to which a fetus is exposed. There are still many things we do not know about the effects of many exposures.

Keep in mind:

  • Fifty per cent of pregnancies are unplanned.
  • Many of the exposures listed below are associated with a risk of a fetus developing a birth defect. This does not mean that an unborn baby exposed to the specific teratogen will develop a birth defect.
  • This information does not take the place of medical care and advice from a health care provider.

Below is a list of some teratogens that may have an effect on a baby during pregnancy.


  • Mercury exposure during pregnancy can affect a baby’s brain development
  • A fetus is much more sensitive to mercury than an adult
  • The USA Environmental Protection Agency/Food and Drug Administration has the following advisory regarding fish consumption and mercury:
    o Do not eat: Shark, swordfish, King Mackerel, Tilefish
    o Do eat: up to 12oz/wk (two average meals) of a variety of fish and shellfish that are lower in mercury
    o Fish commonly low in mercury: shrimp, canned light tuna, salmon, Pollock, catfish
  • For specific guidelines on fish consumption see: (see page 48)


  • Even women whose diabetes is well controlled appear to be at threefold excess risk of major birth defects than non-diabetic women – why this still happens is still unknown.
  • The risk of having a baby with a birth defect greatly increases in women who are unable to control their blood sugar levels.
  • It appears there is no increased risk of having a child with a major birth defect for women who have gestational diabetes.


  • Alcohol affects fetal development.
  • Alcohol exposure during pregnancy increases the risk of major birth defects which include brain damage, heart defects, eye defects and others
  • Many things will influence the effects that alcohol will have on any given child: the quantity of alcohol consumed, the time period over which the alcohol was consumed, the mother's genetic make-up and her ability to digest alcohol, the baby's genetic make-up and his/her ability to digest alcohol, the mother's nutritional status (if she is eating well or has any deficiencies), etc.
  • The fetus is vulnerable throughout the pregnancy therefore any reduction in alcohol consumption at any stage of pregnancy is good.
  • It is estimated that 1% of all births in Canada and the USA are affected by Fetal Alcohol Spectrum Disorder (FASD).
  • FASD is underdiagnosed.
  • The safest choice for a pregnant or breastfeeding woman is to drink no alcohol at all.
  • Early identification of FASD leads to interventions, services and improved outcomes.


 (Selective Serotonin Reuptake Inhibitor) for treatment of depression

  • Data is inconsistent but some specific SSRIs have been linked to specific birth defects, e.g., paroxetine has been linked to cardiac defects in babies of mothers who were prescribed and took paroxetine.
  • Very little data exists on neurobehavioral impacts on school aged children whose mothers took antidepressants during pregnancy.

Maternal infections

  • The following table is a brief summary indicating whether the infection stated is known to cause birth defects in some babies. Not all babies exposed to an infection in the first column will be born with a birth defect, even if mom has this infection while pregnant.

Can have a teratogenic effect

No known teratogenic effect

May have a teratogenic effect

Cytomegalovirus (CMV)



Rubella (German measles)



Varicella (Chicken pox)

Coxsackie virus






Lyme Disease





Rubella/German measles

  • A mother who is infected with rubella, also known as the German measles, in her first trimester has a high risk of passing the infection on to her fetus.
  • After the fourth month of pregnancy the fetus is less likely to be harmed by the virus.
  • A fetus infected in the first trimester has a high risk of being born with congenital rubella syndrome, which can include: heart defects, eye defects, intellectual disability, growth retardation, and deafness.
  • Prevention is the best defense against congenital rubella syndrome. It is recommended that children are vaccinated against rubella with the MMR vaccine.
  • Women who are not immune to rubella and are planning a pregnancy should be vaccinated with the MMR vaccine at least 28 days before becoming pregnant. The vaccine contains a live virus; therefore women who are pregnant should not be vaccinated.


  • Obese women have double the risk of the general population of having a child with a neural tube defect (NTD), such as spina bifida.
  • Obese women also have a small but increased risk for having a baby with a heart defect or cleft palate.
  • The risk to the baby increases as the woman’s BMI increases (BMI is Body Mass Index and is calculated according to the following formula: (weight in kg) / (height in meters)2).
  • The reasons why an obese woman is at a greater chance of having a baby with a birth defect is unknown.
  • Obesity during pregnancy can contribute to the childhood – adolescent – adult obesity cycle.


  • Was used to treat symptoms (such as morning sickness) in early pregnancy in the 1950s and early 1960s.
  • Was found to cause severe birth defects, the most recognizable of which were severe defects to baby’s arms and legs.

Local resources on teratogens:

  • Yukon’s Alcohol and Drug Services
    6118 6th Avenue
    Whitehorse, Yukon
    Business hours:
    From Whitehorse (8:00 am – 4:30 pm)    667-5405
    From communities, no charge (8:00 am – 4:30 pm) 1-855-667-5777 local 5405
    For after-hours support:
    From Whitehorse (4:30 pm – 8:00 am) 667-8473
    From communities, no charge (4:30 pm – 8:00 am) 1-855-667-5777 local 8473
    Fax:    867-667-8471
  • CASY – Congenital Anomalies Surveillance Yukon
    Business hours:
    Contact: Shannon Ryan
    Tuesday - Friday from 9:00 am – 3:30 pm 
    From Whitehorse 667-8563
    From communities, no charge 1-800-661-0408, ext. 8563

Online resources on teratogens


  • provides information about the risk or safety of prescription and over-the-counter drugs, herbal products, chemicals, x-rays, chronic disease and infections during pregnancy and while breastfeeding for mothers and health care providers
  • Motherisk helplines (available 9am-5pm EST Mon-Fri)
    1-877-327-4636 Alcohol and Substance (available 9am-5pm in all Canadian time zones Mon-Fri)
    1-800-436-8477 Morning Sickness
    1-888-246-5840 HIV and HIV Treatment
    1-877-439-2744 Motherisk Helpline
    416-813-6780 Motherisk Helpline


  • Free resource
  • Info on medication and herbal supplement safety, drugs of abuse, alcohol, chemicals, illnesses and more during pregnancy and breastfeeding

Online resources for fish consumption:


The information in this resource was mainly compiled from information gathered at the Human Teratogens: Environmental Factors which Cause Birth Defects Conference held in April 2013 in Boston, Massachusetts and sponsored by the Genetics Unit, MassGeneral Hospital for Children and the Department of Continuing Education, Harvard Medical School.



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