How Smoking Impacts Foetal Brain and Lung Development

The gestational period is a crucial phase during which environmental exposures can impair the unborn baby’s development. Cigarette smoking during pregnancy exposes the foetus to more than 7,000 chemicals, including the neurotoxin nicotine and the respiratory toxin carbon monoxide. These chemicals can easily cross the placenta and harm the foetal nervous system and lungs by disrupting normal cellular differentiation. This article aims to delineate the impacts of smoking on the baby.

Foetal Brain Structure and Function Disruption

Maternal cigarette smoking and passive smoking during pregnancy can severely harm foetal health. There is significant development of the structure and functions of the foetus’ brain, as neurons are proliferated, migrate, and form sophisticated synaptic connections. Maternal smoking and secondhand smoke inhibit the developmental process in the following ways:

Nicotinic Receptors Malfunction

Nicotine is a foreign substance that triggers many of the same reactions as acetylcholine, a key neurotransmitter involved in early brain development. Nicotine exposure during pregnancy can impair neuronal differentiation, the process through which progenitor cells develop into functional neurons. This disruption also affects other neurotransmitter systems involved in emotional regulation and cognition.

Brain Structure Modification and Volume Reduction

Several neuroimaging studies indicate that maternal smoking during pregnancy causes significant structural changes in the developing brain. These include:

• Brain Volume Reduction: Individuals exposed to maternal smoking before birth tend to have reduced volume sizes in the frontal lobes and cerebellum.

• Cortical Atrophy: The risks of smoking during pregnancy include lower cerebral grey and white matter volume, surface area reduction, and gyration.

• Microstructure Modulation: Maternal smoking can alter the integrity of the foetal brain’s white matter, impairing the development of neural connections.

Neurodevelopmental Disorders

The structural modifications in the developing brain lead to various neurodevelopmental disorders. A large Korean mother-infant cohort study involving more than 860,000 mother-child pairs found that maternal smoking is a significant and modifiable risk factor for Attention-Deficit/Hyperactivity Disorder (ADHD). Although associations were also observed with Autism Spectrum Disorder (ASD) and intellectual disabilities, the evidence linking maternal smoking to ADHD was the strongest.

Impaired Development of Foetal Lungs and Respiratory Functioning

Among all the body systems, smoking’s impact on foetal lung development is the most damaging. The lethal compounds of tobacco smoke make newborns susceptible to chronic respiratory problems.

Modifications in Lung Structure

The impact of smoking on fetal lung development can be observed through the effects of nicotine and carbon monoxide on both the physical development and biochemical composition of the lungs. Key changes include:

• Incomplete Alveolarization: Babies born to mothers who smoke often have fewer, and larger alveoli, reducing the total surface area available for gas exchange.

• Limited Attachment Sites: A lower number of alveolar-bronchiolar junctions contributes to airflow obstruction and increased airway sensitivity.

• Elevated Collagen Formation: The higher levels of nicotine cause collagen formation in the lung parenchyma, contributing to stiffer, less compliant lung tissue.

Biochemical and Immunological Damage

Exposure to toxins in cigarette smoke during pregnancy comes with multiple biochemical changes to the developing foetal lungs, which include effects on surfactant production in the lungs and inflammation pathways.

• Surfactant deficiency: Research in sheep models suggests that exposure to secondhand smoke during the third trimester decreases the production of surfactant protein A (SP-A), an important protein involved in innate immune defence.

• Increased Oxidative Stress: Smoking during pregnancy increases oxidative stress in the developing fetal lungs. Nicotine and carbon monoxide result in the buildup of free radicals, unstable molecules that damage cells, in the foetal lungs. The fetus’ antioxidant defences are overpowered, causing structural, functional, and molecular damage.

Other Risks of Smoking During Pregnancy

In addition to affecting the baby’s brain and lungs, maternal smoking causes physiological stress and long-lasting molecular changes that can adversely affect the baby’s growth and development.

Chronic Foetal Hypoxia

Since the effects of carbon monoxide on the foetus are more pronounced on haemoglobin as compared to oxygen, carboxy becomes abundant in the umbilical arteries; therefore, oxygen supply to the foetus is hindered. Chronic hypoxia is one of the leading causes of intrauterine growth restriction (IUGR) and poor development of organs.

Low Birth Weight

When an expectant woman smokes, toxins are emitted and prevent the baby from growing properly. Carbon monoxide in cigarettes removes oxygen from the blood, while nicotine, on the other hand, constricts blood vessels, reducing the amount of nutrients reaching the baby. As a result, low birth weight occurs. In addition, developmental problems arise, and the death rates can be higher.

Premature Birth

Smoking during pregnancy leads to complications such as placental abruption, in which the placenta separates prematurely from the uterine wall, and placenta previa, where the placenta partially or completely covers the cervix. Both conditions can necessitate premature birth or birth before the 37^th week. Further, smokers experience the risk of Premature Rupture of Membranes (PPROM), which leads to preterm labour.

Conclusion

Maternal smoking has a profound and lasting impact on foetal brain and lung development. Avoiding active and passive smoking is imperative to safeguard the respiratory and neurodevelopmental health of the baby.