Find out what can harm your unborn baby

Some substances, organisms and processes may harm your baby during pregnancy. We call these things teratogens. These can be:

  • diseases;
  • medications;
  • drugs;
  • alcohol; or
  • environmental exposures.

Things that can have an impact on the effects of teratogens on an unborn baby, include:

  • when during a pregnancy an unborn baby is exposed to something; and
  • the dose that an unborn baby receives.

There are still many things we do not know about the effects of teratogens on an unborn baby.

What to keep in mind

  • 50% of pregnancies are unplanned.
  • The information on this page does not take the place of medical care and advice from your health care provider.
  • The examples we give below are things that may affect an unborn baby, including causing a birth defect.
  • Even if an unborn baby is exposed to these things it does not mean they will definitely develop a birth defect.

Things that may affect a baby during pregnancy



  • The risk of having a baby with a birth defect greatly increases if you're unable to control your blood sugar levels.
  • Even if your diabetes is well-controlled, your baby is 3 times more at risk of having major birth defect.
  • If you do not have diabetes but develop high blood sugar levels during pregnancy (gestational diabetes) your baby is not at risk of having a major birth defect.


  • Alcohol affects an unborn baby's development.
  • If you're pregnant or breastfeeding your safest choice is to drink no alcohol at all.
  • Your baby is vulnerable throughout your pregnancy.
  • Any reduction in alcohol consumption at any stage of pregnancy is good.
  • Alcohol exposure during pregnancy increases the risk of major birth defects which include:
    • brain damage;
    • heart defects; and
    • eye defects.
  • Many things will influence the effects that alcohol will have on a baby, including:
    • the quantity of alcohol consumed;
    • the time period over which the alcohol was consumed;
    • your genetic make-up and your ability to digest alcohol;
    • your baby's genetic make-up and their ability to digest alcohol; and
    • if your eating well or has any deficiencies.
  • About 1% of all births in Canada and the United States are affected by fetal alcohol spectrum disorder (FASD).
  • People with fetal alcohol spectrum disorder are not always diagnosed.
  • Diagnosing fetal alcohol spectrum disorder early means people with this disorder can get help to reach their full potential.

Selective Serotonin Reuptake Inhibitor

  • People take selective serotonin reuptake inhibitors (SSRIs) to treat depression.
  • Some SSRIs have been linked to specific birth defects. For example, paroxetine has been linked to cardiac defects in babies of mothers who took paroxetine.
  • Very little information exists on neurobehavioural 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 1st column will be born with a birth defect, even if their mother 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



Human immunodeficiency virus (HIV)



Lyme disease





Rubella (German measles)

  • If you're infected with rubella, also known as the German measles, there's a high risk of passing the infection on to your unborn baby during your 1st trimester.
  • After the 4th month of pregnancy your baby is less likely to be harmed by the virus.
  • If you're baby is infected in the 1st trimester they have 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 defence against congenital rubella syndrome. We recommend that children are vaccinated against rubella with the measles, mumps, and rubella (MMR) vaccine.

If you're not immune to rubella and planning a pregnancy, you should be vaccinated with the MMR vaccine at least 28 days before becoming pregnant. The vaccine contains a live virus and women who are pregnant should not be vaccinated.


We do not know why an obese woman is at a greater chance of having a baby with a birth defect. The risk to your baby increases as your increases body mass index (BMI) increases. BMI is calculated according to the following formula: your weight in kilograms divided by your height in metres; then, this sum is divided by 2.

If you're obese, you're chances of having a child with a neural tube defect (NTD), such as spina bifida is double than that of a non-obese woman. You also have a small but increased risk for having a baby with a heart defect or cleft palate. Obesity during pregnancy can contribute to the childhood – adolescent – adult obesity cycle.


In the 1950s and early 1960s, thalidomide was used to treat symptoms, such as morning sickness, in early pregnancy. The drug caused birth defects, the most recognizable of which were severe defects to a baby’s arms and legs.


If you have questions about pregnancy and alcohol or drug use phone 867-667-5405, or long distance 1-855-667-5777, extension 5405.

If you have questions about other teratogens phone 867-667-8563, or long distance 1-800-661-0408, extension 8563.