Environmental Influences on Prenatal Development

Chapter 3: The Prenatal Period, Birth, and the Newborn: Environmental Influences on Prenatal Development

3.2 Environmental Influences on Prenatal Development

Learning Objective

  • Explain how exposure to teratogens can affect prenatal development, leading to abnormalities or defects.

Overview

  • Prenatal development follows a programmed path characterized by a predictable pattern of change.

  • Environmental factors can disrupt this development process.

  • A teratogen is defined as:

an agent, such as a disease, drug, or another environmental factor, that disrupts prenatal development, increasing the risk of abnormalities, defects, and even death.

  • Teratology is the field that investigates the causes of birth defects to identify how to avoid them.

  • Health care providers are tasked with informing pregnant women and those intending to conceive about teratogens and suggest ways to avoid them, in order to promote healthier outcomes for childbirth.

Principles of Teratology

  • Various teratogens exert different effects on developmental processes.

  • The impact of teratogens can be unpredictable.

Critical Periods

  • The degree of damage caused by teratogen exposure is contingent on the stage of prenatal development during which the exposure occurs.

    • There are critical periods in development when the organism is most susceptible to teratogenic damage (Nelson & Gabard-Durnam, 2020).

    • Stages of susceptibility:

    • Germinal Stage: Exposure can impede cell division and prevent implantation, often going unnoticed as many women are unaware of their pregnancy.

    • Embryonic Period: This period poses the greatest sensitivity, as structural deficits may occur if teratogens are introduced when specific body parts are developing (Webster et al., 2018).

    • After the development of specific body parts, susceptibility decreases, though parts like the brain remain vulnerable throughout the pregnancy.

Dose-Response Relationship

  • The intensity of exposure (dose level) to a teratogen influences the effects experienced during development.

    • General trend: Greater doses and prolonged exposure typically result in increased damage.

    • Certain teratogens demonstrate a strong dose–response relationship; for example, increased alcohol consumption correlates with heightened developmental risks (Bandoli et al., 2019).

Individual Differences

  • Susceptibility to teratogens can vary based on genetic factors and the prenatal environment, including maternal health and nutrition.

  • Responses to teratogens can range widely among individuals:

    • Some may exhibit severe defects, while others may develop more mild anomalies, or in some cases, normal development may occur (Kaminen-Ahola, 2020).

  • Example: Dizygotic (fraternal) twins might show different levels of adverse effects from the same teratogenic exposure (Astley Hemingway et al., 2019).

Complicated Effects

  • Different teratogens may result in similar birth defects, while one single teratogen can lead to a variety of defects.

  • Some effects might not become apparent immediately at birth, emerging later in life (Charness et al., 2016).

    • E.g., infants exposed to diethylstilbestrol (DES), though appearing healthy at birth, faced reproductive health issues as adults, including increased cancer risks (Conlon, 2017).

Types of Teratogens

  • Prenatal development can be influenced by various factors including maternal substance use (drugs), illnesses, and environmental hazards.

  • The decision between using prescription medications and the potential risks to fetus can often present challenging dilemmas for healthcare providers and patients.

    • The health benefits for the mother must be weighed against the risks posed to the fetus.

    • In many cases, continuing treatment with medication might be essential for the mother's well-being, necessitating a balance of risks.

Common Teratogens

  1. Prescription and Non-Prescription Drugs

    • Over 90% of pregnant women take medications during pregnancy (Servey & Chang, 2014).

    • Teratogenic prescription drugs include antibiotics, hormones, antidepressants, anticonvulsants, and certain acne medications (Tsamantioti & Hashmi, 2020).

    • Historical Example: Many women used thalidomide in the late 1950s and early 1960s for morning sickness but suffered severe birth defects.

    • Isotretinoin: Linked to severe structural and developmental anomalies, requiring stringent monitoring (FDA, 2010).

    • Research on OTC medications is still developing, with findings indicating potential adverse effects linked to common pain medicines like aspirin.

  2. Alcohol

    • Alcohol exposure is a leading cause of developmental disabilities (Webster et al., 2018).

    • Fetal Alcohol Spectrum Disorders (FASD) affects an estimated 2% to 5% of schoolchildren in the U.S.

    • Fetal Alcohol Syndrome (FAS): Characterized by distinct facial features, growth deficiencies, and cognitive deficits, lasting into adulthood.

  3. Cigarettes

    • About 7%-10% of women smoke during pregnancy. Health risks include fetal deaths, low birthweight, and birth defects.

    • Infants exposed to maternal smoking can develop lifelong respiratory and cognitive issues.

  4. E-Cigarettes

    • Use during pregnancy is increasing; the effects include potential bronchial and cognitive impairments (Greene & Pisano, 2019).

  5. Marijuana

    • Between 4% to 7% report use; associated with long-term impacts on fetal growth and cognitive function (Thompson et al., 2016).

  6. Cocaine

    • Known to result in low birthweight, behavioral issues, and cognitive deficits (dos Santos et al., 2018).

  7. Opioids

    • Includes heroin and legal prescriptions; poses risks for newborn withdrawal and long-term development issues.

Maternal Illness Effects

  • Illnesses like rubella can lead to serious defects especially if contracted early in pregnancy.

  • Conditions like STIs (e.g., syphilis, HIV) can also be transmitted during fetal development or through birth, with significant long-term health impacts on the child (McHenry et al., 2008).

Environmental Hazards

  • Exposure to environmental toxins (e.g., lead, mercury) and radiation can drastically impair development, manifesting in cognitive and physical defects.

    • Historical data from atomic bomb exposure reveals extensive birth defects and developmental issues in affected populations.

Contextual Factors and Teratogens

  • Teratogen exposure often happens alongside exposure to numerous other risks, complicating assessment of their individual effects.

  • Policies regarding maternal drug use can disproportionately affect marginalized groups, often deterring them from seeking necessary medical care.

Ethical and Policy Implications

  • Criminalizing substance use during pregnancy raises significant ethical concerns, affecting women of color and those from low socioeconomic backgrounds disproportionately.

  • Effective maternal health strategies must include supportive rather than punitive measures to ensure better outcomes for both mother and child.