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Prescription Medicine during Pregnancy
To Take or Not to Take?
Deciding whether to use medication during pregnancy can be challenging. While some medicines appear to be harmless during pregnancy, others increase the risk of birth defects or cause other problems. Some prescriptions may not initially appear to be detrimental but have the potential to affect your child in the distant future. Clearly, it is important to learn about the safety of taking medication during pregnancy.

If you have a medical condition that requires medical treatment, you must weigh the risks of taking medication against the benefits of properly treating your condition. Common health conditions that require ongoing treatment include depression, thyroid imbalance, high blood pressure, AIDS, diabetes and asthma. Appropriate medical therapy for these conditions during pregnancy will provide the healthiest start for your baby. It is essential to discuss your medical situation with your doctor as soon as you know you are pregnant so that suitable therapy can be planned.

Determining Drug Safety
Your doctor will help you choose the safest medication to use during pregnancy. Most medication enters your blood circulation and can cross the placenta by a process called “diffusion,” eventually reaching your baby. Factors affecting drug transport across the placenta include the size of the drug molecule (larger molecules may not cross), whether it is bound to a protein carrier (only “free” molecules cross) and whether it dissolves better in water or lipid (fat). If a drug cannot cross the placenta, it will not be able to reach your baby. If a drug crosses the placenta easily, your baby can be exposed to significant levels.

Timing of drug exposure
Your baby goes through different stages of development, and the same medication can have different effects on your growing baby at different time periods. The time in which your baby develops its major organs is known as the critical period of development. This occurs from the second through the eighth week after conception, and is the time when a baby is most vulnerable to major birth defects. (Unfortunately, many women do not realise they are pregnant for several weeks and inadvertently take medication during this period.) Exposure to medication later in pregnancy may not cause any problems or may have subtle effects on growth or behaviour rather than causing birth defects.

Learning about the Effects of Medication in Pregnancy
Scientists learn about the effects of drugs through research on animals and on adult human volunteers. However, well-controlled research studies on drug effects are rarely done on pregnant women. Instead, anecdotal information is collected on the experiences of mothers who have been taken medication during pregnancy. Though this information is helpful, the information it provides is limited. In order to gain more information about drug safety in pregnancy, pregnancy registries have been established to allow researchers to study the experience of many women already using medication during pregnancy. The FDA (Food and Drug Administration) has a guide on current pregnancy registries at http://www.fda.gov/womens/registries.

Current Safety Information
The FDA created a rating system to help assess the risk of drug use during pregnancy.

Category A: These have been tested for safety in pregnancy, and have not shown a risk to the fetus. The possibility of a drug in this category being harmful to a fetus is very low. Medication in this category includes vitamin B-6, folic acid and thyroid medication.

Category B: These medications are not thought to pose a risk during pregnancy based on animal studies and limited human data, and are probably safe to use. Most antibiotics are in this category.

Category C: Drugs in this category have either been shown to cause adverse fetal effects in animal studies, or studies in women and animals are not available. These drugs should only be given if the potential benefits justify the potential fetal risks. Examples of these drugs are prochlorperazine (Compazine), pseudoephedrine (Sudafed) and some antidepressants.

Category D: There is clear evidence of human fetal risk with these medications. However, these drugs may be used treat serious or life-threatening disease during pregnancy. Examples include lithium (to treat manic-depressive illness) and most chemotherapy agents (used to treat cancer).

Category X: These drugs have clearly shown birth defects in humans and/or animals, and the risk of this drug use during pregnancy absolutely outweighs any possible benefit. Examples include the medication for cystic acne (Accutane) or diethylstilbestrol (DES).

If you require medication for a medical condition and are currently pregnant or planning a pregnancy, I strongly urge you to consult with a physician and discuss potential effects of medication use. If you would like to learn more about the effects of specific medication during pregnancy, the following websites are helpful.


Organization of Teratogenic Information Services

centre for the Evaluation of Risks to Human Reproduction (CERHR)

March of Dimes Birth Defects Foundation