AP Syllabus focus:
‘Prenatal development is influenced by teratogens, maternal illness, genetic mutations, and environmental and hormonal factors that affect physical and psychological outcomes.’
Prenatal development is shaped by interacting biological and environmental forces. Psychologists focus on risk and protective factors that alter typical physical growth and brain development, influencing later cognition, emotion, and behavior.
Core idea: risk depends on timing, dose, and vulnerability
This chart summarizes the “critical/sensitive periods” during prenatal development, showing when specific organ systems are most vulnerable to teratogens. The red warning markers highlight weeks when exposure is most likely to produce structural abnormalities, while the brain/spinal cord remains sensitive across a longer span of gestation. Use it to connect the concept of timing to real outcomes (e.g., why early exposure can disrupt organ formation). Source
Prenatal influences rarely act in isolation. Effects tend to vary with:
Timing (which developing systems are most sensitive at that moment)
Dose/intensity (amount and frequency of exposure)
Genetic vulnerability (some fetuses are more susceptible than others)
Co-occurring risks (e.g., poor nutrition plus substance exposure)
Teratogens (harmful external agents)
What teratogens are and how they act
Teratogen: Any harmful agent (such as a drug, chemical, pathogen, or radiation) that can disrupt prenatal development and produce birth defects or later developmental problems.
Teratogens can interfere with cell division, oxygen delivery, and neural development, raising risk for structural abnormalities and neurodevelopmental outcomes.
High-yield teratogen examples
Alcohol: a leading preventable cause of prenatal brain injury; risk increases with heavier and binge patterns.
Nicotine/tobacco: associated with low birth weight, preterm birth, and later attention/behavior difficulties.
Other drugs (including some prescription/illicit substances): may affect withdrawal at birth and later self-regulation.
Environmental toxins (e.g., lead, mercury, some pesticides): can impair CNS development.
Radiation: at sufficient exposure, increases risk of growth restriction and malformations.
Alcohol and long-term functioning
Fetal Alcohol Spectrum Disorders (FASD): A range of physical, cognitive, and behavioral impairments caused by prenatal alcohol exposure, varying in severity.
A key AP Psychology emphasis is that prenatal alcohol exposure can produce lifelong changes in learning, impulse control, and adaptive functioning, not just visible physical effects.
Maternal illness and infection
Maternal health can shape development through fever/inflammation, reduced oxygenation, and direct fetal infection.
Viral infections (e.g., rubella) can increase risk for sensory impairments and congenital anomalies.
Zika virus is linked to atypical brain development, including microcephaly.
Untreated sexually transmitted infections may contribute to complications (e.g., prematurity) and neonatal illness.
Chronic maternal conditions (e.g., poorly controlled diabetes, hypertension) can alter fetal growth patterns and birth outcomes.
Psychologically, prenatal exposure to severe maternal illness can increase risk for later cognitive delays and emotional/behavioral dysregulation, partly via effects on the developing brain.
Genetic mutations and chromosomal abnormalities
Genetic factors influence development directly and can also moderate sensitivity to environmental risks.
Genetic mutations may arise spontaneously during cell division and can affect protein formation critical for development.
Chromosomal abnormalities (often from nondisjunction) can alter physical growth and cognitive functioning (e.g., trisomy conditions).
Outcomes often include a mix of physical features, medical complications, and learning differences that vary widely across individuals.
A practical takeaway is that “genetic” does not mean “unchangeable”: supportive environments and early intervention can still improve functional outcomes.
Environmental and hormonal factors
Nutrition and physical environment
Maternal malnutrition can restrict fetal growth and is linked to later health and cognitive risks.
Micronutrients matter: inadequate folic acid increases risk of neural tube defects.
This labeled cross-sectional diagram shows the embryo’s neural folds and neural groove during closure (panel A) and the closed neural tube covered by surface ectoderm (panel B). It visually explains how early disruptions in closure can lead to neural tube defects affecting the brain and spinal cord. Linking this to nutrition, adequate folate availability is especially important during these early closure processes. Source
Pollution/toxic exposure (air pollution, heavy metals, endocrine disruptors) can affect birth weight and neurodevelopment.
Hormonal influences
Hormonal conditions shape fetal development and can “program” stress and metabolic systems.
Elevated prenatal exposure to stress hormones (especially cortisol) is associated with differences in infant reactivity and later anxiety/attention risk.
Maternal thyroid hormones support brain development; disruption can affect cognitive outcomes.
Physical and psychological outcomes (what may be affected)
Prenatal influences can alter:
Physical outcomes: growth restriction, congenital anomalies, low birth weight, prematurity
Brain/CNS development: altered connectivity and executive functioning
Psychological outcomes: learning and memory differences, attention problems, increased risk for mood/behavior disorders, difficulty with self-regulation
Protective factors include consistent prenatal care, avoidance of known teratogens, infection prevention/treatment, adequate nutrition, and early screening when risks are present.
FAQ
The placenta filters and transports substances between mother and fetus, but many chemicals (including alcohol) cross it.
Transport depends on molecule size, solubility, and dose.
Yes. Sperm quality can be influenced by age, toxins, and some illnesses.
Paternal epigenetic marks may alter gene expression after conception.
They combine animal evidence, human observational studies, dose–response patterns, and biological mechanisms.
Randomised experiments are usually unethical in pregnancy.
Differences include genetics, maternal metabolism, timing of exposure, nutrition, and co-occurring stressors.
Protective caregiving after birth can also reduce later impairment.
Structural defects are visible anatomical changes (e.g., organ malformations).
Neurodevelopmental effects involve brain-based functioning (e.g., attention, learning, inhibition), sometimes without obvious physical signs.
Practice Questions
Define a teratogen and give one example of a teratogen that can affect prenatal development. (2 marks)
1 mark: Accurate definition of teratogen (harmful agent disrupting prenatal development).
1 mark: Correct example (e.g., alcohol, nicotine, rubella virus, radiation, lead).
Explain how (i) prenatal exposure to alcohol and (ii) maternal infection can influence both physical and psychological outcomes. Include the role of timing of exposure and one protective factor. (6 marks)
1 mark: Alcohol exposure identified as a teratogen affecting development.
1 mark: Physical outcome linked to alcohol (e.g., growth restriction/characteristic physical anomalies).
1 mark: Psychological outcome linked to alcohol (e.g., executive function/attention/learning difficulties; FASD).
1 mark: Maternal infection explained as a prenatal influence (pathogen/inflammation affecting fetus).
1 mark: Physical or psychological outcome linked to infection (e.g., congenital impairment, atypical brain development, later cognitive delay).
1 mark: Timing importance (different systems vulnerable at different points) AND/OR a protective factor (e.g., prenatal care, vaccination, prompt treatment, avoiding alcohol).
