During your first prenatal visit, your health care provider will discuss how you can adjust your lifestyle to ensure the best possible outcome for your pregnancy. Your provider will encourage you to eat a well-balanced diet and gain weight appropriately. Most importantly, you should avoid chemicals that can affect the developing baby. If you smoke, drink alcohol, or use recreational drugs, you should try to quit as soon as you suspect you are pregnant. These substances can affect the developing baby throughout all stages of pregnancy (as well as during breast-feeding).

Critical periods of organ development (when chemicals cause the most damage).Highly sensitive periods (in weeks)
Organ system affected2.5 - 6.5
Heart3.0 - 5.5
Central nervous system3.5 - 7.0
Limbs3.5 - 7.5
Eyes3.5 - 8.5
Ears6.5 - 8.0
Teeth6.5 - 8.5

Substances that can cause abnormal fetal development are known as teratogens. In addition to alcohol, some prescription and over-the-counter medications and certain infections can act as teratogens. You should inform your health care provider of all the medications and supplements you are using so that she can ensure that none of these substances are potential teratogens.