Many women take medications during pregnancy and lactation. Studies have shown that most women take at least 1 medication during their pregnancy. The use of multiple medications during pregnancy is increasing. Some drugs are required during pregnancy to treat certain disorders. Your provider will weigh the known benefits versus risks to consider the treatment of your disorder during pregnancy.  

Most drugs cross the placenta and do this via the same route that oxygen and other nutrients cross to reach the fetus. Drugs may affect the fetus in different ways. They may cause direct damage or may trigger preterm labor by causing the uterus to contract. Drugs can also indirectly affect the fetus due to the mother’s health. For example, drugs that lower the mother’s blood pressure may also reduce blood flow to the placenta and may reduce the amount of oxygen that is delivered to the fetus. The effect that a drug has on the placenta and the fetus depends on many different factors.  This can include the gestational age of the fetus, the strength and dose of the drug, and the mother’s overall health.

In 1979, the FDA created a letter-based system to describe the potential of a drug to cause birth defects if used during pregnancy.  These categories were A, B, C, D, or X. They explained whether a drug was safe or not during pregnancy. For example, Category B designation indicated that animal reproductive studies have failed to demonstrate a risk to the fetus and that there are no adequate or well-controlled studies in pregnant women. Category X drugs were at the other end of the spectrum and had evidence of fetal harm and the risks of using the drug outweighed any benefit. This category is contraindicated in pregnancy. It is good to remember that much of the data used to assign these categories were based on animal studies, which may or may not always be relevant to human use.

In 2015, the FDA created a new system of interpreting pregnancy-related drug safety information that replaced the letter-based system. This was called The Pregnancy and Lactation Labeling Rule (PLLR) and helped to standardized how information about drug use in pregnancy was presented. There is now more human data presented, which helps to support the clinical relevance of drug safety in pregnancy.  Although this new labeling does improve the old format, it still does not give a definitive yes or no answer. Patients must still speak to their providers and clinical interpretation may still be required. Also, the package inserts (the information provided with a prescription drug that lists risks and benefits of the product) now contains a “Pregnancy” section that summarizes risks of negative side effects. This narrative text replaced the single-letter descriptor A, B, C, D, or X.

The FDA designed The Pregnancy and Lactation Labeling Rule to provide healthcare providers and patients with useful and clear information related to prescription medication use. Hopefully, this new information will make the interpretation of drug use in pregnancy easier than the old system. If you have any questions about the risks to yourself or your unborn baby of any drug, always ask your doctor or pharmacist.

Have you ever had to make a difficult decision to start or stop medication in pregnancy? Did your provider guide you and go over these guidelines? 

Natasha Stamper is a clinical pharmacist and online fertility coach. She found her love for all things fertility while living in a remote Alaska village navigating her own IVF journey alone. After many miscarriages, two ectopic pregnancies, and one cervical ectopic she had her two miracle babies. Now with over 12 years of clinical pharmacy experience and her own experiences she is so excited to be helping families all over the globe fulfill the dream of making their family complete. You can find her on Instagram at fertility_pharmacist or