The Importance of Medication Review in Pregnancy
Medication use during pregnancy is extremely common, with studies showing that up to 80% of pregnant women report taking at least one medicine [1.6.1]. While many medications are necessary for managing chronic conditions or acute illnesses, others can pose significant risks to a developing fetus. A substance that interferes with normal fetal development, causing birth defects, is known as a teratogen [1.5.2]. Exposure to teratogenic drugs, especially during the first trimester when vital organs are forming, can lead to structural or functional abnormalities [1.5.4]. Therefore, a thorough evaluation of all medications—including prescriptions, over-the-counter (OTC) drugs, and herbal supplements—is a critical component of prenatal care.
Understanding FDA Pregnancy Risk Assessment
For decades, the U.S. Food and Drug Administration (FDA) used a letter-based system (Categories A, B, C, D, and X) to classify the fetal risk of drugs [1.3.7]. Category A was considered the safest, while Category X drugs were contraindicated because their risks clearly outweighed any potential benefits [1.3.5]. However, this system was often misinterpreted as a simple grading scale and lacked nuance [1.3.3].
In 2015, the FDA replaced the letter categories with the Pregnancy and Lactation Labeling Rule (PLLR) [1.3.1, 1.3.2]. The PLLR requires drug labels to provide a more detailed narrative summary of the risks. This new format includes three main subsections:
- Pregnancy: Information includes a risk summary, clinical considerations, and data from human and animal studies. It also notes the existence of any pregnancy exposure registries [1.3.9].
- Lactation: This section provides information about using the drug while breastfeeding, such as the amount of drug in breast milk and potential effects on the infant [1.3.9].
- Females and Males of Reproductive Potential: This new section discusses the need for pregnancy testing, contraception recommendations, and information about the drug's effects on fertility [1.3.4].
This shift aims to provide healthcare providers with better, more comprehensive information to facilitate risk-benefit discussions with their patients [1.3.1].
High-Risk Prescription Medications to Avoid
Certain classes of prescription medications are well-documented to be harmful during pregnancy. It is essential to discuss any of these with a healthcare provider, ideally before conception.
ACE Inhibitors and Angiotensin II Receptor Blockers (ARBs)
Used to treat high blood pressure, drugs like lisinopril (an ACE inhibitor) and losartan (an ARB) are contraindicated, especially during the second and third trimesters [1.5.7]. They can cause fetal kidney damage, low amniotic fluid (oligohydramnios), incomplete skull ossification, and even fetal death [1.2.2, 1.5.7].
Certain Anticonvulsants
While managing seizures is crucial during pregnancy, some anticonvulsants are highly teratogenic. Valproic acid (Category X) is associated with neural tube defects like spina bifida and developmental delays [1.2.5, 1.5.7]. Phenytoin and carbamazepine (Category D) are linked to a collection of birth defects known as fetal hydantoin syndrome, which can include craniofacial abnormalities and limb defects [1.5.1, 1.5.7].
Isotretinoin and Other Retinoids
Isotretinoin, a powerful drug used for severe acne, is one of the most well-known human teratogens (Category X) [1.2.1]. Exposure can cause severe birth defects affecting the brain, heart, and face [1.5.1]. Even large doses of Vitamin A, a related compound, can be teratogenic [1.2.2].
Warfarin
This anticoagulant (blood thinner) is known to cross the placenta and can cause fetal warfarin syndrome, characterized by skeletal abnormalities (especially of the nose) and brain damage [1.2.2, 1.5.1]. Safer alternatives like heparin are typically used during pregnancy [1.2.5].
Methotrexate
Used for some autoimmune diseases and cancers, methotrexate is a folic acid antagonist that can cause miscarriage and a specific pattern of birth defects affecting the skull, face, limbs, and central nervous system [1.2.6, 1.5.5].
Certain Antibiotics
Tetracyclines can cause permanent discoloration of teeth and affect bone growth in the fetus [1.5.1]. Fluoroquinolones are generally avoided due to concerns about cartilage damage shown in animal studies.
Cautious Use of Over-the-Counter (OTC) Medications
"Over-the-counter" does not automatically mean "safe for pregnancy." Many common OTC products contain ingredients that should be used with caution or avoided entirely.
- NSAIDs (Nonsteroidal Anti-Inflammatory Drugs): Ibuprofen (Advil, Motrin) and naproxen (Aleve) should be avoided, especially after 20 weeks of pregnancy [1.4.3]. Use in the third trimester can cause premature closure of a major fetal blood vessel (the ductus arteriosus) and lead to kidney problems in the baby [1.4.3, 1.4.8]. Acetaminophen (Tylenol) is generally considered the safer choice for pain and fever relief [1.4.5].
- Decongestants: Oral decongestants like pseudoephedrine and phenylephrine are often not recommended, particularly in the first trimester, due to a potential link to certain birth defects [1.4.1, 1.4.4]. Saline nasal sprays are a safer alternative [1.4.2].
- Bismuth Subsalicylate: Found in products like Pepto-Bismol, this medication should be avoided as it is related to aspirin [1.2.7].
- Herbal Supplements: Many herbal remedies are not well-regulated or studied for safety in pregnancy. Products like St. John's wort, dong quai, and goldenseal should be avoided [1.2.1].
Comparison Table: High-Risk vs. Safer Alternatives
| Condition Treated | High-Risk Medication to Avoid | Generally Safer Alternative (with doctor's approval) |
|---|---|---|
| Pain / Fever | Ibuprofen, Naproxen (especially after 20 weeks) [1.4.3] | Acetaminophen (Tylenol) [1.4.5] |
| High Blood Pressure | ACE Inhibitors (e.g., Lisinopril), ARBs (e.g., Losartan) [1.5.7] | Labetalol, Methyldopa [1.2.6] |
| Blood Clot Prevention | Warfarin (Coumadin) [1.2.5] | Heparin, Enoxaparin (Lovenox) [1.2.5] |
| Severe Acne | Isotretinoin [1.2.1] | Topical azelaic acid, topical erythromycin |
| Seizures | Valproic Acid [1.2.5] | Consultation required for alternatives like Lamotrigine [1.2.6] |
| Nasal Congestion | Oral Pseudoephedrine, Phenylephrine [1.4.1] | Saline nasal spray, steam inhalation [1.4.2] |
Conclusion
The fundamental principle of pharmacology during pregnancy is to make a careful risk-benefit analysis for every medication. No drug, supplement, or herbal remedy should be started or stopped without first consulting a healthcare provider [1.2.1]. An untreated maternal health condition can also pose a risk to the fetus, so managing health is paramount. Open communication between the patient and their medical team is the best way to navigate the complex question of which medications should not be administered to pregnant patients, ensuring the healthiest possible outcome for both mother and baby.
For more authoritative information, a useful resource is The FDA's Guide to Medicine and Pregnancy [1.6.1].
