The Food and Drug Administration (FDA) has established a system for ranking drugs according to their probable safety when used during pregnancy. These drugs are listed in five categories:

• Category A. Drugs tested for safety during pregnancy and considered to be safe. They include:
  
  
• • Folic acid
  • Vitamin B6
  • Thyroid medication (taken in moderation)
    
    
• Category B. Drugs used often during pregnancy that do not appear to cause major birth defects or other problems. These include:
  
  
• • Some antibiotics
  • Aspartame (an artificial sweetener)
  • Famotidine (used to treat stomach conditions)
  • Prednisone (cortisone)
  • Insulin (a diabetes medication)
    
    
• Category C. Drugs that are more likely to cause problems for the mother or the fetus, although safety studies have not been completed for many of these medications. These are drugs that should be used only when health benefits outweigh risks, and include:
  
  
• • Some antidepressants (used to treat anxiety disorders and depression)
  • Several drugs used to treat vaginal yeast infections
  • Pseudoephedrine (a cold medication)
  • Ciprofloxacin (an antibiotic)
    
    
• Category D. Drugs that have clear health risks for the fetus. These include:
  
  
• • Alcohol
  • Nicotine
  • Lithium (used to treat bipolar disorder)
  • Phenytoin (an anticonvulsant)
  • Most chemotherapy drugs
    
    
• Category X. Drugs that have been shown to cause birth defects and that should never be taken during pregnancy. A prescribing physician might insist that a patient use a reliable form of contraception while taking these medications known to cause severe birth defects. These drugs include:
  
  
• • Thalidomide (used to treat leprosy and being studied to treat other diseases)
    
    
  • Certain drugs used to treat skin conditions such as cystic acne and psoriasis
    
    
  • Diethylstilbestrol (DES, a synthetic estrogen previously used to prevent miscarriage)

Other drugs that have been classified using FDA guidelines to determine their safety during pregnancy include:

Over-the-counter pain medications

Over-the-counter decongestants,
expectorants and antihistamines

Over-the-counter antidiarrheal medications

Over-the-counter antacid preparations

Over-the-counter vaginal antifungal medications

Aspirin – one of the most commonly used drugs in the world – and other drugs containing salicylate should not be used during pregnancy, particularly during the third trimester. The World Health Organization (WHO) has also stated that nursing mothers should not use aspirin, as it may be transferred through breast milk to the baby. Aspirin is associated with Reye syndrome, a rare condition that affects the brain and liver in children who receive aspirin during a viral illness. Other conditions associated with the use of salicylates during pregnancy include:

• Perinatal mortality
• Neonatal hemorrhage
• Decreased birth weight
• Prolonged gestation and labor
• Possible birth defects
  

However, some high-risk pregnancy conditions call for the use of low dose aspirin (baby aspirin) during a pregnancy, and this can be used safely under close medical supervision. Also, acetylsalicylate – a common ingredient in many over-the-counter painkillers – may cause pregnancy to last longer, and may increase the risk of severe bleeding prior to and after delivery.

In addition to medicines, other types of drugs and supplements may pose dangers to women during pregnancy. These include:

• Herbal remedies and supplements. The safety of herbal remedies and supplements during pregnancy is largely unknown, as they are not required by the FDA to undergo rigorous testing. However, these products may contain agents that can harm the fetus or cause difficulties during the pregnancy. Thus, herbal products should not be taken unless a physician approves their use.
  
  
• Recreational drugs. Legal and illegal recreational drugs may pose danger to a pregnant woman. These include:
  
  
• • Nicotine and other chemicals in tobacco products. Smoking is associated with higher incidences of miscarriage, stillbirth, bleeding, premature birth and low birth weight. It has also been linked to sudden infant death syndrome (SIDS), a disorder in which infants suddenly die for no apparent reason. Smoking while pregnant can also have long-term ramifications for the physical growth and intellectual development of children.
    
    
  • Alcohol. A pregnant woman who drinks alcohol may trigger fetal alcohol syndrome (FAS), which causes problems in the fetus such as mental slowness, poor growth rates, facial defects and head size that is smaller than normal. Women should not drink before or during pregnancy, or while nursing.
    
    
  • Illegal drugs. Marijuana, cocaine and other illegal drugs raise the risk of miscarriage, premature birth and birth defects. Use of some drugs can cause the child to be born with a physical addiction to the substance that may result in withdrawal symptoms after birth.

Pregnant women generally should limit themselves to one or two cups daily of drinks that contain caffeine. Caffeine easily passes through the placenta to the fetus, and levels of caffeine stay elevated longer in the fetus than in the mother. It can also pass through breast milk and cause agitation in nursing babies.