Can Prescription Drugs Considered to Be Safe Affect My Pregnancy?

Prescription Drugs Pregnancy

A pregnant woman nowadays is more likely to be taking medication compared to her mother or grandmother, with studies showing medication use during pregnancy increasing in the US by more than 60 percent over the last three decades. In addition, a recent study showed that 82 percent of women fulfilled medication prescriptions during the course of their pregnancy and around 42 percent of pregnant women were dispensed a medication potentially harmful to the fetus. However, this may have been in the period before the woman knew she was pregnant or the healthcare provider may have carefully weighed up the pros and cons for the mother and baby of prescribing these drugs.

What data exist regarding drug safety during pregnancy?

Although a drug may be prescribed by your healthcare provider or is available over-the-counter, this doesn’t necessarily mean that it is safe to take during pregnancy. Some drugs do have evidence of harm to the fetus, such as the blood thinner warfarin (Coumadin and generic formulations), the acne drug isotretinoin (Sotret, Absorica), cholesterol-lowering statins, and the ulcer drug called misoprostol (Cytotec and generic formulations). However, for the majority of drugs, the risks of taking them during pregnancy are unknown. In fact, only two of the 54 prescription and over-the-counter drugs most commonly used by women during pregnancy have been studied enough to confidently know whether or not they pose a risk to the fetus, according to a 2013 study conducted by the Centers for Disease Control and Prevention. Absence of data does not mean that a drug is safe and, although you can find lists of drugs on Internet that are considered safe for pregnant women, many of these were included in these lists solely because do not have evidence of harm. However, lack of harm is not necessarily the same as being safe!

Aren’t drugs tested on pregnant women?

Women who are pregnant or who may become pregnant are almost always excluded from clinical trials due to safety and/or liability concerns. As an alternative, drugs are tested in animals to see whether they cause birth defects. However, although these animal studies give some idea, the outcomes are not entirely accurate in predicting effects on the human fetus.

In 2007, Congress authorized the FDA to require drug manufacturers to study the effects on the fetus of newly approved medications. The main way drug companies do this is through patient registries that collect and maintain data on approved drugs for diseases such as HIV/AIDS, cancer, diabetes, and asthma. Pregnant or nursing women taking these medications can then join these registries and researchers can then compare data from these women to data from women taking the same drugs who are not pregnant.

Read here about pregnancy registries and why you may be a good candidate to participate in one of them.

How do drugs affect the fetus?

Drugs can have various effects on the developing fetus, with the type and severity of harm often depending on when the pregnant woman takes the drug. In the first week of conception and before implantation, a drug tends to have an all or nothing effect – that is, either the embryo implants without an issue or the pregnancy is lost.

Once implantation has occurred, the embryo is at risk of the medication crossing the placenta and entering the baby’s bloodstream. The most severe birth defects often occur during the first trimester, especially during weeks 2 through to 8 when the baby’s organs are developing. During the second and third trimesters, certain medications, such as acetaminophen (Tylenol or other generic formulations), can affect the growing brain of the fetus.  A study of acetaminophen conducted in Denmark  in more than 64,000 children found that children who were exposed to acetaminophen in the womb were more likely to have behavioral problems. Although these effects were more severe in children whose mothers took acetaminophen for longer than 7 days and in the second and third trimesters.

Is it better to not take medications at all?

For minor illnesses, such as the common cold, it is possible to relieve the symptoms without the use of medications such as decongestants or antihistamines. Instead you can:

  • Drinking plenty of liquids
  • Getting adequate rest
  • Sucking on nonmedicated lozenges
  • Gargling salt water

However, for many women going off their medication is not an option and this can even cause greater harm to the fetus than staying on a medication. For example, many women with asthma tend to try and reduce the drugs they are taking to control it; however, this can be detrimental to the fetus as uncontrolled asthma can result in pregnancy complications, such as high blood pressure, placental issues, preterm birth and babies with low birth weights. Epilepsy is another example whereby it is safer for the fetus if the mother takes medication rather than stopping it and risking a seizure.

Consequently, women with chronic health conditions, such as asthma, diabetes, depression, or epilepsy should work closely with their healthcare provider to come up with a plan that reduces potential harm to the fetus but also controls the disease in question. Questions that you can ask your healthcare provider include:

  • What are the risks of my condition to my pregnancy?
  • What medications should I continue to take?
  • What medications should I stop taking?
  • What medications can be swapped for one that is safer during pregnancy?

Regarding this last point, sometimes temporarily switching to another drug may be the best option. In general, older drugs with a long history of safe use during pregnancy are recommended over newer drugs which may be more effective but which are often lacking safety data during pregnancy. If a safer alternative is not possible, then discuss whether you can reduce your dose or discontinue the drug during the period in which it is most likely to cause harm. However, make sure that you are monitored closely if either of these measures is taken so as to ensure your condition isn’t going to affect your baby.

Melody Watson
Melody Watson holds Bachelors degrees in Biochemistry and Microbiology. She works as a medical writer for a medical communications agency in Berlin, Germany, where her work ranges from medical translation to writing publications for medical journals. Melody is passionate about promoting science, including evidence-based medicine, and debunking pseudoscience.

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