Foetal Exposure During Pregnancy

When a pregnant woman is exposed to certain substances or environmental factors, her developing baby can be affected in ways that last a lifetime. Understanding what these exposures are and how they impact fetal development is crucial for protecting the health of both mother and child.

Table of contents

• Understanding Foetal Exposure
• Alcohol Exposure During Pregnancy
• Radiation Exposure During Pregnancy
• Medication and Drug Exposure
• Why Timing of Exposure Matters
• Prevention and Risk Reduction

Understanding Foetal Exposure

Foetal exposure refers to situations where a developing baby comes into contact with substances or environmental factors that can affect its growth and development while still in the womb. These harmful substances are called teratogens, which are anything a pregnant woman is exposed to or ingests during pregnancy that is known to cause abnormalities in the developing embryo or fetus.^[12]

The impact of these exposures depends on several important factors. The type of substance or toxin, how long the exposure lasted, the amount of exposure (dosage or quantity), the stage of pregnancy when exposure occurred, and hereditary factors all play a role in determining how dangerous the exposure might be.^[12] When a pregnant woman breathes in or swallows harmful substances, they enter her bloodstream and can pass through the placenta to reach the baby.^[23]

Studies show that exposure to teratogens accounts for about 4% to 5% of congenital disorders, which are conditions present at birth. Research has also demonstrated that exposure to teratogens affects both cognitive and physical development.^[12]

Alcohol Exposure During Pregnancy

Alcohol is one of the most well-studied and dangerous substances a pregnant woman can consume. When a woman drinks any amount of alcohol during pregnancy—including wine, beer, hard ciders, and liquor—it passes through her bloodstream to the fetus through the umbilical cord.^[4] The baby’s body does not break down alcohol the same way an adult’s does, meaning it stays in the baby’s system longer and causes more damage.

Alcohol exposure during pregnancy can result in fetal alcohol spectrum disorders (FASD), which refers to a wide range of physical, behavioral, and cognitive impairments that occur due to alcohol exposure before birth. These impairments may appear at any time during childhood and last a lifetime.^[1] Research estimates that 1% to 5% of U.S. first graders have FASD.^[1]

Alcohol can disrupt development at any stage, even before a woman knows she is pregnant. The substance interferes with the development of the baby’s brain and other critical organs and physiological functions, leading to deficits after birth and beyond.^[1] Research shows that binge drinking (consuming multiple drinks in a short period) and heavy drinking during pregnancy put a developing baby at the greatest risk for severe problems. However, even smaller amounts can cause harm.^[1]

The most severe condition within FASD is fetal alcohol syndrome (FAS). Children with FAS may experience a range of symptoms including distinctive facial features (small eyes, a very thin upper lip, a flat nose bridge), slow physical growth before and after birth, delayed development milestones, vision or hearing problems, smaller than average head and brain size, changes in heart, kidney and bone development, poor coordination or balance, and hyperactivity.^[2]

There is no known safe amount of alcohol consumption during pregnancy, and there is no safe time during pregnancy to drink alcohol.^[5] All types of alcohol can be harmful. Alcohol use during pregnancy is also associated with an increased risk of miscarriage, preterm birth, stillbirth, and sudden infant death syndrome (SIDS).^[5]

Radiation Exposure During Pregnancy

Pregnant women may be exposed to radiation through necessary medical procedures, workplace exposure, or diagnostic procedures performed before the pregnancy is known. Radiation can be divided into two main categories: nonionizing radiation and ionizing radiation.^[7]

Nonionizing radiation includes microwave, ultrasound, radio frequency, and electromagnetic waves. Studies have shown that exposure to nonionizing radiation during pregnancy is not associated with significant health risks. This means that ultrasonography (ultrasound) is safe to perform during pregnancy when it is medically indicated and when the lowest possible exposure setting is used.^[7]

Ionizing radiation, which includes particles and electromagnetic radiation such as gamma rays and x-rays, is more concerning. The human embryo and fetus are sensitive to ionizing radiation at doses greater than 0.1 gray (Gy). Depending on the stage of fetal development, exposure at doses greater than 0.5 Gy can be severe, even if such a dose is too low to cause an immediate effect for the mother.^[6]

Based on observations from victims of high levels of radiation exposure (such as survivors of the Hiroshima bombing and the Chernobyl nuclear disaster), the consequences of radiation exposure can be grouped into four categories: pregnancy loss, malformation, developmental delay, and cancer development.^[3] Pregnancy loss most often happens when radiation exposure occurs during early pregnancy (less than two weeks after conception). Malformations and developmental delays occur during organogenesis (the period when organs are forming, from 2 to 8 weeks after conception) and depend on the radiation dose.^[3]

The fetus is most susceptible to radiation during organogenesis and in the early fetal period (eight to 15 weeks after conception). However, noncancer health effects have not been detected at any stage of pregnancy after exposure to ionizing radiation of less than 0.05 Gy (5 rad).^[7] In the United States, the recommended total fetus exposure during pregnancy is less than 5.0 mSv (500 mrem), and radiation doses below 50 mGy are considered safe and not expected to cause harm.^[3]

Medication and Drug Exposure

Prescription drug use is common during pregnancy, yet there is limited knowledge about maternal-fetal safety and efficacy because pregnant individuals have historically been excluded from clinical trials.^[11] This has resulted in a lack of data available to estimate or predict fetal drug exposure accurately.

Certain over-the-counter and prescription medications are considered teratogens. Examples include antiepileptic drugs, antimicrobials, anticoagulants (blood thinners), antithyroid medications, vitamin A (a common ingredient in skincare products), and hormonal medications.^[12] Healthcare providers must weigh the potential benefits and risks of prescription drug use to determine what poses less risk to the pregnancy. In some cases, a medication may have negative impacts on the fetus but may be medically necessary for the mother’s health.^[12]

Cigarette smoking is another significant concern. Smoking is associated with fetal growth restriction, premature birth, and miscarriage. Tobacco smoke affects the fetus’s sensitive lung tissue and brain.^[12] About 5% of pregnant women use recreational substances such as cocaine, methamphetamines, heroin, and marijuana during pregnancy. These can cause low birth weight, heart problems, and neonatal abstinence syndrome, which is when a baby goes through drug withdrawal after birth.^[12]

Why Timing of Exposure Matters

The timing of exposure to harmful substances during pregnancy is critically important. Alcohol, for example, can cause problems for the baby throughout pregnancy, including before a woman knows she is pregnant. Alcohol use in the first 3 months of pregnancy can cause the baby to have abnormal facial features. Growth and central nervous system problems (such as low birthweight and behavioral problems) can occur from alcohol use at any time during pregnancy. The baby’s brain is developing throughout pregnancy and can be affected by exposure to alcohol at any time.^[5]

For radiation exposure, the fetus is most vulnerable during the period of organogenesis (two to seven weeks after conception) and in the early fetal period (eight to 15 weeks after conception). The effects are directly related to the level of exposure and stage of fetal development.^[7] At higher exposure levels, spontaneous abortion, growth restriction, and mental retardation may occur, though the risk of cancer is increased regardless of the dose.^[7]

Teratogenic exposure is generally more damaging at certain times in fetal development. The gestational age of the fetus at the time of exposure is one of the key factors determining how dangerous the exposure will be.^[12]

Prevention and Risk Reduction

Many harmful exposures during pregnancy can be prevented with proper planning and awareness. Women who are pregnant or trying to become pregnant should see a healthcare provider for preconception counseling. This visit allows for discussion about diet and exercise, any factors that increase the risk of having a child with a birth defect, and any special care that may be needed before or during pregnancy.^[21]

To reduce the risk of harmful exposures, pregnant women should avoid all alcohol consumption. It is never too late to stop alcohol use during pregnancy—stopping will improve the baby’s health and well-being.^[5] If a woman cannot stop drinking on her own, she should contact her healthcare provider, local Alcoholics Anonymous, or a local alcohol treatment center for help.^[5]

For radiation exposure, most diagnostic medical exams and occupational exposures within regulatory limits are not likely to cause health effects for the fetus.^[6] When medically necessary imaging tests are required during pregnancy, the benefits often outweigh the risks, and diagnostic studies should not be avoided solely due to fear of radiation exposure, especially when these studies can dramatically change patient management.^[3]

Regarding medications, it is important to tell healthcare providers about any medications being taken, including over-the-counter drugs and supplements. Women should read labels before taking any medication and, when in doubt, call their healthcare provider before taking any substance.^[12]

Additional preventive measures include maintaining a healthy weight, taking a daily multivitamin containing at least 400 micrograms of folic acid before and during pregnancy, managing medical conditions before pregnancy, not using recreational drugs, preventing infections, and avoiding known harmful agents.^[21] For women living in homes built before 1978, it is important to assume the home contains lead paint and to reduce lead hazards, as lead exposure can pass to the developing baby and affect brain development.^[23]

Early diagnosis and proper prenatal care are essential. Making regular visits to healthcare providers allows for monitoring of the pregnancy and addressing any concerns about potential exposures. If exposure to a harmful substance has occurred, healthcare providers can help estimate the level of exposure and counsel about potential risks, allowing informed decisions about pregnancy management.^[7]