Embryology · Teratology and prenatal diagnosis

Ionizing radiation, tobacco and cocaine !

Teratogen

Three exposures with different effects: radiation depends on the week and the dose; tobacco and cocaine affect the placenta and growth.

Updated 2026-11-01

See it in 3D: Frontal lobe

What it is

Ionizing radiation kills rapidly dividing cells: depending on the week it can cause pregnancy loss, malformations, microcephaly and intellectual disability, and it slightly raises the risk of childhood cancer. Routine diagnostic imaging usually gives the fetus exposures far below harmful thresholds. Tobacco and cocaine act mostly through vasoconstriction and hypoxia: growth restriction, preterm birth, placental problems and some birth defects.

Key facts

Deterministic effects (malformation, restriction, disability) have a threshold, and it rises as pregnancy advances.
The stochastic effect (childhood cancer, mostly leukaemia) has no threshold, although low-dose evidence is debated.
Among pregnant survivors of the atomic bombs there were miscarriages and severe central nervous system defects.
E-cigarettes and other nicotine products are not safe in pregnancy either.
Women who use cocaine often also use alcohol, which makes the effects hard to attribute.

Critical period and mechanism

Radiation: damages DNA and kills proliferating cells; in weeks 8–15 after conception it disturbs neuronal proliferation and migration.
Tobacco: nicotine constricts uterine vessels and carbon monoxide lowers the oxygen reaching the fetus.
Cocaine: intense vasoconstriction and hypertension that reduce placental flow and can interrupt the blood supply of fetal tissues.
Critical period: radiation depends on the week; tobacco and cocaine harm throughout pregnancy.

Prevention

Asking about possible pregnancy before radiation studies; using radiation-free techniques when equally useful.
Not postponing needed studies out of fear; the treating team weighs the balance.
Stopping smoking and avoiding cocaine and other substances before and during pregnancy, with professional support.

What it does to the embryo and fetus

Radiation: miscarriage, microcephaly, intellectual disability, growth restriction, eye defects.
Tobacco: growth restriction, preterm birth, cleft lip and palate, higher risk of sudden infant death.
Cocaine: placental abruption, preterm birth, growth restriction, miscarriage.
Cocaine: heart, genitourinary and brain malformations, and possible long-term behavioural effects.

Test yourself

Think of the answer, then tap the question to see it.

In which period does radiation carry the highest risk of microcephaly and intellectual disability?

Weeks 8 to 15 after conception, while cortical neurons proliferate and migrate.

How do deterministic and stochastic radiation effects differ?

Deterministic effects (malformation, disability) occur only above a threshold; the stochastic effect (childhood cancer) has no threshold.

Why does tobacco cause fetal growth restriction?

Nicotine constricts the vessels and carbon monoxide lowers the oxygen reaching the fetus.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

Frontal lobe

← All of embryology

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Radiation Effects on the Fetus (StatPearls Publishing (NCBI Bookshelf), 2023); Substance Use During Pregnancy (CDC, 2024); Langman's Medical Embryology, 13th ed., ch. 9: Birth Defects and Prenatal Diagnosis (Wolters Kluwer, 2015).

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Representative model, for educational purposes only.