During pregnancy, women may need to take medications to treat new or existing health conditions. Also, certain vitamins are recommended during pregnancy. Before taking any medication (including over-the-counter medications) or dietary supplement (including medicinal herbs), a pregnant woman should consult a doctor. Women currently taking medications and planning to become pregnant should consult a doctor before pregnancy, if possible, to see if those medications need to be stopped or changed. (See also the Centers for Disease Control and Prevention: Medicine and Pregnancy.)
Medications or other substances taken by a pregnant woman may reach the fetus by crossing the placenta, the same route taken by oxygen and nutrients, which are needed for the fetus's growth and development. However, those that do not cross the placenta may still harm the fetus by affecting the uterus or the placenta.
Medications or other substances that a pregnant woman takes during pregnancy can affect the fetus in several ways:
No impact on the fetus and its development
Act directly on the fetus, causing damage, abnormal development (leading to birth defects), or death
Alter the function of the placenta, usually by causing blood vessels to narrow (constrict) and thus reducing the supply of oxygen and nutrients to the fetus from the mother (sometimes resulting in the baby being underweight and underdeveloped)
Cause the muscles of the uterus to contract forcefully, indirectly injuring the fetus by reducing its blood supply or triggering preterm labor and delivery
Affect the fetus indirectly (for example, medications that lower the mother's blood pressure may reduce blood flow to the placenta and thus reduce the supply of oxygen and nutrients to the fetus)
How Medications Cross the Placenta
Some of the fetus's blood vessels are contained in tiny hairlike projections (villi) of the placenta that extend into the wall of the uterus. The mother's blood passes through the space surrounding the villi (intervillous space). Only a thin membrane (placental membrane) separates the mother's blood in the intervillous space from the fetus's blood in the villi. Medications in the mother's blood can cross this membrane into blood vessels in the villi and pass through the umbilical cord to the fetus. |
How a medication affects a fetus depends on the
Stage of fetal development
Strength and dose of the medication
Permeability of the placenta (how easily substances pass through it)
Genetic factors in the pregnant woman, which affects how much of the medication is active and available
Pregnant woman's health (for example, nausea and vomiting may decrease absorption of a medication taken by mouth)
Government agencies that oversee drug safety may classify medications based on current knowledge about safety during pregnancy. In the United States, the US Food and Drug Administration (FDA) provides information about drug safety in pregnancy (see FDA: Medicine and Pregnancy). Knowledge about drug safety in pregnancy is based on research in humans and animals and on side effects that are reported by people who have taken the medication. In general, doctors advise pregnant women about taking a medication based on available research, importance of the medication to the health of the pregnant woman, and whether there are other treatments that have less risk to the pregnant woman or fetus. Medications are given in pregnancy if the benefits outweigh the risks.
Vaccines During Pregnancy
Immunization is as effective in women who are pregnant as in those who are not. (See also Centers for Disease Control and Prevention (CDC): Pregnancy and Vaccination.)
Vaccines made with a live virus (such as the rubella vaccine and varicella vaccine) are not given to women who are or might be pregnant.
Other vaccines (such as those for cholera, hepatitis A, hepatitis B, plague, rabies, and typhoid) are given to pregnant women only if they are at substantial risk of developing that particular infection and if the risk of side effects from the vaccine is low.
Some vaccines that are considered safe in pregnant women and are recommended during pregnancy include
Influenza (flu) vaccine for all women who will be or are pregnant during the flu season
Tetanus-diphtheria-pertussis (Tdap) vaccine (protects against pertussis [whooping cough]) during the third trimester of each pregnancy
COVID-19 vaccination for people who are pregnant, breastfeeding, trying to get pregnant, or might become pregnant in the future
Evidence about the safety and effectiveness of COVID-19 vaccination during pregnancy has been growing. These data suggest that the benefits of receiving a COVID-19 vaccine outweigh any known or potential risks of vaccination during pregnancy. (See also CDC: COVID-19 Vaccines While Pregnant or Breastfeeding.)
In August 2023, the US Food and Drug Administration (FDA) approved use of a respiratory syncytial virus (RSV) vaccine in pregnant individuals between 32 to 36 weeks of pregnancy, with a warning to avoid use prior to 32 weeks (see FDA Approves First Vaccine for Pregnant Individuals to Prevent RSV in Infants).
Medications Used to Treat Heart and Blood Vessel Disorders During Pregnancy
Medications to lower high blood pressure (antihypertensives) may be needed by pregnant women who have had high blood pressure before pregnancy or who develop it during pregnancy. Either type of high blood pressure increases the risk of problems for a (such as preeclampsia) and for the fetus (see High Blood Pressure During Pregnancy). However, antihypertensives can reduce blood flow to the placenta if they lower blood pressure too rapidly in pregnant women. Pregnant women who have to take these medications are closely monitored.
Several types of antihypertensives, such as angiotensin-converting enzyme (ACE) inhibitors and thiazide diuretics, are usually not given to pregnant women. These medications can cause serious problems in the fetus, such as kidney damage, inadequate growth before birth (growth restriction
heart failure and some abnormal heart rhythms, readily crosses the placenta. But at the usual doses, digoxin typically has little effect on the baby before or after birth.
Antidepressants During Pregnancy
Clinical depression is common during pregnancy and, therefore, antidepressants
Paroxetine appears to increase the risk of heart birth defects. So if a pregnant woman takes paroxetine, echocardiography should be done to evaluate the fetus's heart. However, other SSRIs do not increase this risk.
If a pregnant woman takes antidepressants, the newborn may have withdrawal symptoms (such as irritability and shaking) after delivery. To prevent these symptoms, doctors may gradually reduce the dose of the antidepressant during the third trimester and stop the medication before the baby is born. However, if a woman has significant signs of depression or if symptoms worsen as the dose is reduced, antidepressants should be continued. Depression during pregnancy can lead to postpartum depression, which involves a serious change in mood and requires treatment.
Medications Used During Labor and Delivery
Medications used to relieve pain during pregnancy (such as local anesthetics and opioids) usually cross the placenta and can affect the newborn. For example, they can weaken the newborn's urge to breathe. Therefore, if these medications are needed during labor, they are given in the smallest effective doses.
