Birth Defects: Causes, Risks, and How Medications Affect Fetal Development

When a baby is born with a physical or functional abnormality, it’s called a birth defect, a structural or functional problem present at birth that can affect any part of the body. Also known as congenital anomalies, these conditions range from minor issues like a small skin tag to serious problems like heart malformations or neural tube defects. About 1 in 33 babies in the U.S. is born with one, and while many are caused by genetics or random events, a significant number are linked to what the mother takes during pregnancy.

Placental drug transfer, the process by which substances move from the mother’s bloodstream into the developing fetus plays a huge role. Not all drugs cross the placenta the same way—size, solubility, and how tightly they bind to proteins determine how much reaches the baby. Some medications, like certain antidepressants or acne treatments, are known to interfere with fetal development. Others, like nitrofurantoin for urinary infections, are considered safe in early pregnancy. Teratogenic risk, the chance that a substance will cause birth defects isn’t just about the drug itself—it’s about timing, dose, and the mother’s health. That’s why fetal medication exposure, the amount and type of drugs a fetus is exposed to during critical growth windows is studied through pregnancy registries and real-world data.

Some birth defects happen because of a single exposure, like thalidomide in the 1950s, while others come from long-term use of multiple medications. Gestational diabetes, if not managed, can lead to heart or spine problems in babies. Even something as simple as a high fever in early pregnancy can increase risk. That’s why knowing what’s safe—and what’s not—isn’t just helpful, it’s life-changing. The posts below dive into exactly that: which drugs cross the placenta, how pregnancy registries track real outcomes, what alternatives exist for risky medications, and how to talk to your doctor without fear or guilt. You’ll find clear, practical info on everything from hydroxyzine’s cardiac risks to how St. John’s Wort can interfere with treatments during pregnancy. No fluff. Just what you need to make smarter choices.