Abnormal Development - Smoking

Notice - Mark Hill

Currently this page is only a template and will be updated (this notice removed when completed).

Introduction

There is an association between physical defects among newborns and maternal smoking tobacco during pregnancy.

Spontaneous abortion, pre-term births, low-weight full-term babies, and fetal and infant deaths all occur more frequently among mothers who smoke during pregnancy than among those who do not. These developmental abnormalities are therefore maternal in origin and not congenital (though there are probably genetics involved with a tendency to smoke).

The possible relationship to preterm birth generates one major clinical problem, as preterm birth results in 47% of all neonatal deaths (UK data).

Also of great concern is that smoking is a suggested causative factor for low infant birth weight (LBW) (2.500kg and below). LBW is in turn related to future (postnatal) health by the fetal origins hypothesis.

Some Recent Findings

Quantitative effects of tobacco smoking exposure on the maternal-fetal circulation "In pregnant women who smoke, higher arterial resistance indices and lower birth weights were observed, and these findings were associated with increasing levels of tobacco smoking exposure. The values were significantly different when compared to those found in non-smoking pregnant women. This study contributes to the findings that smoking damage during pregnancy is dose-dependent, as demonstrated by the objective methods for measuring tobacco smoking exposure."

Nicotine

Nicotine is a natural ingredient in tobacco leaves, where as an alkaloid it provides some protection for the plant being eaten by insects by acting as a botanical insecticide.

Tobacco also contains other minor alkaloids nornicotine, anatabine and anabasine.

There is a chemical datasheet for nicotine, the pure chemical, note that commercial tobacco products include many additional chemicals.

Neonates have a decreased ability to metabolise nicotine, with a 3-4 times longer half-life in newborns exposed to tobacco smoke compared with adults.

Cytochrome P450, Subfamily IIA, Polypeptide 6 (CYP2A6) is the main enzyme in the liver responsible for metabolism (oxidation) of nicotine. (More? OMIM Entry CYP2A6) and there are known mutations that occur in this gene which would also impact on nicotine metabolism.

See also the recent review paper Metabolism and disposition kinetics of nicotine. Hukkanen J, Jacob P 3rd, Benowitz NL. Pharmacol Rev. 2005 Mar;57(1):79-115. | Dempsey D, Jacob P 3rd, Benowitz NL. Nicotine metabolism and elimination kinetics in newborns. Clin Pharmacol Ther. 2000 May;67(5):458-65. | OMIM Entry CYP2A6

Carbon Monoxide

Smoking tobacco is also a source of carbon monoxide (CO), a colourless and odorless gas formed mainly as a by-product of incomplete combustion of hydrocarbons and can cause cytotoxicity by tissue hypoxia. A recent study has identified in a newborn mouse model, effects on neurodevelopment of even sub-clinical levels of carbon monoxide.

Carbon monoxide:

• enters circulation though the respiratory system
• binding to haemoglobin to form carboxy-haemoglobin (COHb)
  • haemoglobin affinity is 240 times greater than for oxygen
  • fetal haemoglobin binds with even greater affinity
• tissue hypoxia occurs when COHb levels are greater than 70%

Australian National Drug Strategy Household Survey 1995

Below are excerpted statistics from the 1995 household survey.

Smoking is higher among young women than young men, although males tend to smoke more heavily. Among 14-19 year olds: 13% are current regular smokers, 5% are occasional smokers, while 49% have never smoked.

For more information please email CEIDA Information Centre

Passive Smoking

Exposure of non-smokers to environmental tobacco smoke, "passive smoking", has been associated with a substantial increased disease risk (coronary heart disease, cancer) a recent study now adds diabetes to the possible deletirious effects. Houston TK, Kiefe CI, Person SD, Pletcher MJ, Liu K, Iribarren C. Active and passive smoking and development of glucose intolerance among young adults in a prospective cohort: CARDIA study. BMJ. 2006 May 6;332(7549):1064-9. "These findings support a role of both active and passive smoking in the development of glucose intolerance in young adulthood."

Smoking and Pregnancy

Smoking doubles the risk of having a low-birthweight baby and significantly increases the rate of perinatal mortality and several other adverse pregnancy outcomes. The mean reduction in birthweight for babies of smoking mothers is 200 g. High quality interventions to help pregnant women quit smoking produce an absolute difference of 8.1% in validated late-pregnancy quit rates. If abstinence is not achievable, it is likely that a 50% reduction in smoking would be the minimum necessary to benefit the health of mother and baby. Healthcare providers perform poorly in antenatal interventions to stop women smoking. Midwives deliver interventions at a higher rate than doctors. The efficacy of nicotine replacement therapy has not been established in pregnancy. Currently, its use should only be considered in women smoking more than 10 cigarettes per day who have made a recent, unsuccessful attempt to quit and who are motivated to quit. Relapse prevention programs have shown little success in the postpartum period. Data from: Quitting smoking in pregnancy Raoul A Walsh, John B Lowe, Peter J Hopkins (MJA 2001; 175: 320-323)

Placental Function

A review of three placental markers showed "maternal smoking impairs human placental development by changing the balance between cytotrophoblast (CTB) proliferation and differentiation"

References

Reviews

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Articles

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Cite this page: Hill, M.A. (2024, April 18) Embryology Abnormal Development - Smoking. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Abnormal_Development_-_Smoking

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G