Drug Use During Pregnancy

ByRavindu Gunatilake, MD, Valley Perinatal Services;

Avinash S. Patil, MD, Center for Personalized Obstetric Medicine, Valley Perinatal Services, Phoenix Last full review/revision November 2018 by Ravindu Gunatilake, MD; Avinash S. Patil, MD

 

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More than 50% of pregnant women take prescription or nonprescription (over-the-counter) drugs or use social drugs (such as tobacco and alcohol) or illicit drugs at some time during pregnancy, and use of drugs during pregnancy is increasing. In general, drugs should not be used during pregnancy unless necessary because many can harm the fetus. About 2 to 3% of all birth defects result from drugs that are taken to treat a disorder or symptom.

Sometimes drugs are essential for the health of the pregnant woman and the fetus. In such cases, a woman should talk with her doctor or other health care practitioner about the risks and benefits of taking the drug. Before taking any drug (including over-the-counter drugs) or dietary supplement (including medicinal herbs), a pregnant woman should consult her health care practitioner. A health care practitioner may recommend that a woman take certain vitamins and minerals during pregnancy.

Drugs taken by a pregnant woman reach the fetus primarily by crossing the placenta, the same route taken by oxygen and nutrients, which are needed for the fetus's growth and development. Drugs that a pregnant woman takes during pregnancy can affect the fetus in several ways:

• They can act directly on the fetus, causing damage, abnormal development (leading to birth defects), or death.
  
• They can 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 the result is a baby that is underweight and underdeveloped.
  
• They can cause the muscles of the uterus to contract forcefully, indirectly injuring the fetus by reducing its blood supply or triggering preterm labor and delivery.
  
• They can also affect the fetus indirectly. For example, drugs 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 Drugs 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. Drugs 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 drug affects a fetus depends on

• The fetus's stage of development
  
• The strength and dose of the drug
  
• The genetic make-up of the mother, which affects how much of the drug is active and available
  
• Other factors related to the mother (for example, if the mother is vomiting, she may not absorb as much of a drug, so the fetus is exposed to less of the drug)
  

 

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Timing and the Effects of Drugs During Pregnancy

 

Until recently, the Food and Drug Administration (FDA) classified drugs into five categories according to the degree of risk they pose for the fetus if they are used during pregnancy. Drugs were classified from those with the least risk to those that are highly toxic and should never be used by pregnant women because they cause severe birth defects. One example of a highly toxic drug is thalidomide. This drug causes extreme underdevelopment of arms and legs and defects of the intestine, heart, and blood vessels in the babies of women who take the drug during pregnancy.

The FDA's classification system was based largely on information from studies in animals, which often do not apply to people. For example, some drugs (such as meclizine) cause birth defects in animals, but the same effects have not been seen in people. Taking meclizine for nausea and vomiting during pregnancy does not appear to increase the risk of having a baby with a birth defect. The classification system was based much less often on well-designed studies in pregnant women because few such studies have been done. Thus, applying the classification system in specific situations was difficult.

Because of this problem, the FDA eliminated the five risk categories. Instead, the FDA now requires that the drug label include more specific information, which includes the following:

• The risks of taking the drug during pregnancy and breastfeeding
  
• The evidence that has identified these risks
  
• Information to help health care practitioners decide whether the drug should be used during pregnancy and to help them explain the risks and benefits of using the drug to the woman
  

Typically, health care practitioners follow a general rule:

• They consider giving a pregnant woman a drug to treat a disorder only when the potential benefit outweighs known risks.
  

Often, a safer drug can be substituted for one that is likely to cause harm during pregnancy. For prevention of blood clots, the anticoagulant heparin is preferred to warfarin. Several safe antibiotics, such as penicillin, are available to treat infections.

Some drugs can have effects after they are stopped. For example, isotretinoin, a drug used to treat skin disorders, is stored in fat beneath the skin and is released slowly. Isotretinoin can cause birth defects if women become pregnant within 2 weeks after the drug is stopped. Therefore, women are advised to wait at least 3 to 4 weeks after the drug is stopped before they become pregnant.

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Some Drugs That Can Cause Problems During Pregnancy ^*

 

Vaccines During Pregnancy

Immunization is as effective in women who are pregnant as in those who are not.

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.

However, all pregnant women who are in the 2nd or 3rd trimester during the influenza (flu) season should be given the influenza vaccine. All pregnant women should be given the tetanus-diphtheria-pertussis (Tdap) vaccine between 27 and 36 weeks of each pregnancy. This vaccine protects against pertussis (whooping cough).

Drugs Used to Treat Heart and Blood Vessel Disorders During Pregnancy

Drugs 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 the woman (such as preeclampsia) and for the fetus (see page High Blood Pressure During Pregnancy). However, antihypertensives can markedly reduce blood flow to the placenta if they lower blood pressure too rapidly in pregnant women. So pregnant women who have to take these drugs 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 drugs can cause serious problems in the fetus, such as kidney damage, inadequate growth before birth (growth restriction), and birth defects. Spironolactone is also not given to pregnant women. This drug may cause the development of feminine characteristics (feminization) in a male fetus.

Use of thiazide diuretics during pregnancy is controversial. They are not the first antihypertensive used.

Digoxin, used to treat 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

Antidepressants, particularly selective serotonin reuptake inhibitors (SSRIs) such as paroxetine, are commonly used during pregnancy. Use is common because about 7 to 23% of pregnant women have depression. For pregnant women, the benefits of treating depression usually outweigh the risks.

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 3rd trimester and stop the drug before the baby is born.

However, if the 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.

Social Drugs During Pregnancy

Cigarette (tobacco) smoking during pregnancy

Although cigarette smoking harms both pregnant women and their fetus, only about 20% of women who smoke are able to quit during pregnancy.

The most consistent effect of smoking on the fetus during pregnancy is

• A reduction in birth weight (growth restriction)
  

The more a woman smokes during pregnancy, the less the baby is likely to weigh. The average birth weight of babies born to women who smoke during pregnancy is 6 ounces less than that of babies born to women who do not smoke.

Birth defects of the heart, brain, and face are more common among babies of smokers than among those of nonsmokers.

Also, the risk of the following may be increased:

• Sudden infant death syndrome (SIDS)
  
• A mislocated placenta (placenta previa)
  
• Premature detachment of the placenta (placental abruption, or abruptio placentae)
  
• Premature rupture of the membranes (containing the fetus)
  
• Preterm labor
  
• Uterine infections
  
• Miscarriages
  
• Stillbirths
  
• Premature births
  

In addition, children of women who smoke have slight but measurable deficiencies in physical growth and in intellectual and behavioral development. These effects are thought to be caused by carbon monoxide and nicotine. Carbon monoxide may reduce the oxygen supply to the body's tissues. Nicotine stimulates the release of hormones that constrict the vessels supplying blood to the uterus and placenta, so that less oxygen and fewer nutrients reach the fetus.

Because of the possible harmful effects of smoking during pregnancy, pregnant women should make every effort to not smoke during pregnancy, including discussing strategies with their doctor.

Pregnant women should avoid exposure to secondhand smoke because it may similarly harm the fetus.

 

Alcohol during pregnancy

Drinking alcohol during pregnancy is the leading known cause of birth defects. Because the amount of alcohol required to cause fetal alcohol syndrome is unknown, pregnant women are advised to abstain from drinking any alcohol regularly or on binges. Avoiding alcohol altogether is even safer.

 

Did You Know...

The leading known cause of birth defects is drinking alcohol during pregnancy.

The risk of miscarriage almost doubles for women who drink alcohol in any form during pregnancy, especially if they drink heavily.

Often, the birth weight of babies born to women who drink regularly during pregnancy is substantially below normal. The average birth weight is about 4 pounds for babies exposed to large amounts of alcohol, compared with 7 pounds for all babies. Newborns of women who drank during pregnancy may not thrive and are more likely to die soon after birth.

Fetal alcohol syndrome is one of the most serious consequences of drinking during pregnancy. Binge drinking as few as three drinks a day can cause this syndrome. It occurs in about 2 of 1,000 live births. This syndrome includes the following:

• Inadequate growth before birth or after birth
  
• Birth defects of the face
  
• A small head (microcephaly), probably caused by inadequate growth of the brain
  
• Intellectual disability
  
• Abnormal behavioral development
  
• Less commonly, joint abnormalities and heart defects
  

Babies or children of women who drank alcohol during pregnancy may have severe behavioral problems, such as antisocial behavior and attention-deficit/hyperactivity disorder. These problems can occur even when the baby has no obvious physical birth defects.

 

Caffeine during pregnancy

Whether consuming caffeine during pregnancy harms the fetus is unclear. Evidence seems to suggest that consuming caffeine in small amounts (for example, one cup of coffee a day) during pregnancy poses little or no risk to the fetus.

Caffeine, which is contained in coffee, tea, some sodas, chocolate, and some drugs, is a stimulant that readily crosses the placenta to the fetus.

Some evidence suggests that drinking more than seven cups of coffee a day may increase the risk of having a stillbirth, premature birth, low-birth-weight baby, or miscarriage.

Some experts recommend limiting coffee consumption and drinking decaffeinated beverages when possible.

 

Aspartame during pregnancy

Aspartame, an artificial sweetener, appears to be safe during pregnancy when it is consumed in small amounts, such as in amounts used in normal portions of artificially sweetened foods and beverages. For example, pregnant women should consume no more than 1 liter of diet soda a day.

Pregnant women with phenylketonuria, an unusual disorder, should not consume any aspartame.

Illicit Drugs During Pregnancy

Use of illicit drugs (particularly opioids) during pregnancy can cause complications during pregnancy and serious problems in the developing fetus and the newborn. For pregnant women, injecting illicit drugs increases the risk of infections that can affect or be transmitted to the fetus. These infections include hepatitis and sexually transmitted diseases (including AIDS). Also, when pregnant women take illicit drugs, growth of the fetus is more likely to be inadequate, and premature births are more common.

 

Amphetamines during pregnancy

Use of amphetamines during pregnancy may result in birth defects, especially of the heart, and possibly inadequate growth before birth.

Bath salts during pregnancy

Bath salts refers to a group of designer drugs made from various substances that resemble amphetamine. More and more pregnant women are using these drugs.

The drugs may cause the blood vessels in the fetus to narrow, reducing the amount oxygen the fetus gets.

Also, these drugs increase the risk of the following:

• Stillbirth
  
• Premature detachment of the placenta (abruptio placentae)
  
• Possibly birth defects
  

 

Cocaine during pregnancy

Cocaine taken during pregnancy may cause the blood vessels that carry blood to the uterus and placenta to narrow (constrict). Then, less oxygen and fewer nutrients reach the fetus.

If pregnant women use cocaine regularly, risk of the following is increased:

• Miscarriage
  
• Inadequate growth of the fetus
  
• Premature detachment of the placenta (placental abruption, or abruptio placentae)
  
• Premature birth
  
• Stillbirth
  
• Birth defects (including brain and spinal cord, urinary tract, and bone defects)
  

However, whether cocaine is the cause of those problems is unclear. For example, the cause may be other risk factors that are common in women who use cocaine. Such factors include cigarette smoking, use of other illicit drugs, deficient prenatal care, and poverty.

 

Hallucinogens during pregnancy

Hallucinogens may, depending on the drug, increase the risk of the following:

• Miscarriage
  
• Premature delivery
  
• Withdrawal syndrome in the fetus or newborn
  

Hallucinogens include methylenedioxymethamphetamine (MDMA, or Ecstasy), rohypnol, ketamine, methamphetamine, and LSD (lysergic acid diethylamide).

 

Marijuana during pregnancy

Whether use of marijuana during pregnancy can harm the fetus is unclear. The main component of marijuana, tetrahydrocannabinol, can cross the placenta and thus may affect the fetus. However, use of a small amount of marijuana does not appear to increase the risk of birth defects or to slow the growth of the fetus.

Marijuana does not cause behavioral problems in the newborn unless it is used heavily during pregnancy.

 

Opioids during pregnancy

Opioids are used to relieve pain, but they also cause an exaggerated sense of well-being, and if used too much, they can cause dependence and addiction.

Opioids, such as heroin, methadone, and morphine, readily cross the placenta. Consequently, the fetus may become addicted to them and may have withdrawal symptoms 6 hours to 8 days after birth. However, use of opioids rarely results in birth defects.

Use of opioids during pregnancy increases the risk of complications during pregnancy, such as

• Miscarriage
  
• Abnormal presentation of the baby
  
• Preterm delivery
  

Babies of heroin users are more likely to be small.

 

Drugs Used During Labor and Delivery

Drugs 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 drugs are needed during labor, they are given in the smallest effective doses.

 

 

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version