3.7 Pregnancy and smoking

Last updated: March 2015 
Suggested citation: Ford, C, Greenhalgh, EM & Winstanley, MH. 3.7 Pregnancy and smoking. In Scollo, MM and Winstanley, MH [editors]. Tobacco in Australia: Facts and issues. Melbourne: Cancer Council Victoria; 2015. Available from http://www.tobaccoinaustralia.org.au/3-7-pregnancy-and-smoking

 

Smoking during pregnancy is harmful to the health of both the mother and the unborn child. The 2002 United States Linked Birth/Infant Death Data Set reveals that it remains one of the most prevalent preventable causes of infant death and illness.1

In 2010, 11.7% of Australian women smoked during some or all of their pregnancy. In the period before they knew they were pregnant, 11.7% of pregnant women smoked and 7.7% reported that they smoked after they knew they were pregnant. The likelihood of smoking during pregnancy was higher among teenagers, women in disadvantaged circumstances and Indigenous women.2 See Chapter 1, Section 1.10.

Many of the constituents of cigarette smoke are potentially toxic to the developing foetus, including lead, nicotine, cotinine, cyanide, cadmium, mercury, carbon monoxide and polycyclic aromatic hydrocarbons (PAHs).3,4 Carbon monoxide (CO) reduces the oxygen supply to the baby, leading to hypoxia (insufficient oxygen). CO binds to haemoglobin with an affinity 200 times that of oxygen, and also has an inhibiting effect on the release of oxygen to the cells. Chronic mild hypoxia of foetal tissue can persist for five or six hours after the mother has stopped smoking.4 Cadmium, a carcinogen, which accumulates in the placenta and has been detected in umbilical cord blood, is associated with a reduction in foetal capillary volume.4 Nicotine is found in foetal blood, amniotic fluid and breast milk,3 and has short- and long-term effects likely to be related to several adverse pregnancy outcomes.4 Studies suggest that exposure to PAHs may disrupt hormones, alter enzyme levels or activity, and damage DNA, which, if not repaired, can lead to cell death, cancer or foetal abnormalities.4

There are various mechanisms through which smoking may affect the pregnancy and the development of the foetus. Both smoking and nicotine by itself change hormone patterns, affecting the pregnancy outcome and the endocrine profile of the infant. Smoking and nicotine affect the functioning and structure of the oviduct (fallopian tube) in ways that could impair fertilityi and complicate the pregnancy. Smoking disturbs the development of the placenta, disrupting the implantation process and interfering with the transformation of the uterine spiral arteries. Studies consistently show thickening of the villous membrane of the placenta in smokers, which decreases the ability of nutrients to diffuse through the placenta. Smoking and nicotine impair amino acid transport across the placenta, which the baby needs to make foetal proteins. Nicotine may decrease the pumping of fluid across the placenta, leading to lower oxygen levels in the foetus and acidosis (excessive acid in the blood and tissues). Nicotine can alter embryonic movements that are important in the early development of the organs. Consistent evidence shows that smoking can affect the development of the foetal lung and brain. Smoking a cigarette temporarily increases maternal heart rate and blood pressure and decreases foetal heart rate variability (a measure of the infant's wellbeing).4 Studies show a decrease in foetal movement for at least an hour after smoking one cigarette, consistent with a reduction of oxygen to the foetus.5

Smoking may present further risks to the pregnancy by increasing the mother's risk of infectious disease and altering the inflammatory response of her immune system. Smokers have lower levels of micronutrients that play a vital role in the health of the pregnancy, such as zinc (in cord blood) and vitamin C. Vitamin C is important for immune function and the formation of collagen. Genetic variation in enzymes that metabolise chemicals from tobacco smoke mediate the risk of adverse pregnancy outcomes. Several proposed mechanisms for the effects of smoking on pregnancy are presented in more detail in the US Surgeon General's report of 2010.4

3.7.1 Spontaneous abortion

Smoking during pregnancy is associated with spontaneous abortion or miscarriage (the involuntary termination of a pregnancy prior to 20 weeks of gestation).4,6 Because many miscarriages occur too early to be recognised and confirmed, and miscarriage can be caused by a number of preconditions, exposures or events, spontaneous abortions are difficult to study. However there are multiple ways in which smoking could potentially increase the risk for miscarriage. Proposed mechanisms include placental insufficiency, chronic reduced oxygen to the foetus, and direct toxic effects of constituents of cigarette smoke.4Tobacco or nicotine may also affect the quality of the egg and embryonic development.6

3.7.2 Ectopic pregnancy

Maternal active smoking causes ectopic pregnancy (the implantation of a fertilised egg occurring outside the uterus, usually in the fallopian tubes).6  Nicotine slows down the movement of the fertilised ovum in the fallopian tubes, and impairment of oviduct function can lead to ectopic pregnancy.4 Smokers also have a higher risk of developing pelvic inflammatory disease, which is associated with ectopic pregnancy.3 

3.7.3 Complications of pregnancy

Smoking affects the healthy development and function of the umbilical cord and placenta, and causes abnormalities or insufficiencies that can lead to serious complications for the success of the pregnancy and the safe delivery of the baby. Smoking causes premature rupture of the membranes (breaking of the amniotic sac before the onset of labour), placenta previa (when the placenta is attached to the uterine wall close to or over the cervix), and placental abruption (premature separation of the placenta from the wall of the uterus).3,4 These complications increase the risk of preterm delivery, haemorrhaging that requires a blood transfusion, and death of the mother or baby. Research indicates that stopping smoking between pregnancies reduces the risk of placental abruption, suggesting that, for this complication, the effects of smoking do not persist.4

3.7.4 Preterm delivery

Smoking is a cause of preterm delivery (birth at less than 37 completed weeks of gestation) and shortened gestation.3 Preterm delivery is a leading cause of neonatal death and illness.4 Australian data show that in 2003, babies born to mothers who smoked in pregnancy had a 60% higher risk of preterm delivery than babies of non-smoking mothers.7 It is not known how smoking contributes to preterm delivery, but researchers have proposed various mechanisms. Smokers are more susceptible to vaginal infection; for example they have two to three times the risk of bacterial vaginosis, which is a risk factor for preterm delivery. Some research suggests that smokers may be more sensitive to stimuli that lead to contractions. Smoking may affect collagen formation, leading to weakening and rupture of the membranes. Smokers are more likely to develop complications that are risk factors for preterm delivery, such as placental abruption and placenta previa.4

Limited research suggests that women who quit smoking within the first three months of pregnancy reduce their risk of placental complications at birth, premature birth, infant illness and perinatal death.8

Recent news and research

For recent news items and research on this topic, click here (Last updated May 2017 


i Refer to Section 3.6 for discussion of smoking and reproductive health.

References

1. Dietz P, England L, Shapiro-Mendoza C, Tong V, Farr S and Callaghan W. Infant morbidity and mortality attributable to prenatal smoking in the US. American Journal of Preventive Medicine 2010;39(1):45–52. Available from: http://www.ajpm-online.net/article/PIIS074.937.9710002588/fulltext

2. Laws P, Li Z and Sullivan E. Australia's mothers and babies 2008. Perinatal statistics series no. 24, AIHW cat. no. PER 50. Sydney: Australian Institute of Health and Welfare National Perinatal Statistics Unit, 2010. Available from: http://www.aihw.gov.au/publication-detail/?id=644.247.2399&tab=2

3.    US Department of Health and Human Services. The health consequences of smoking: a report of the Surgeon General. Atlanta, Georgia: US Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2004. Available from: http://www.cdc.gov/tobacco/data_statistics/sgr/index.htm

4.    US Department of Health and Human Services. How tobacco smoke causes disease: the biology and behavioral basis for smoking-attributable disease. A report of the US Surgeon General, Atlanta, Georgia: US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2010. Available from: http://www.surgeongeneral.gov/library/tobaccosmoke/report/index.html

5.    US Department of Health and Human Services. The health consequences of involuntary exposure to tobacco smoke: a report of the Surgeon General. Atlanta, Georgia: US Dept. of Health and Human Services, Centers for Disease Control and Prevention, Coordinating Center for Health Promotion, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2006. Available from: http://www.cdc.gov/tobacco/data_statistics/sgr/sgr_2006/index.htm

6.    US Department of Health and Human Services. The health consequences of smoking - 50 years of progress. Atlanta, GA: US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2014. Available from: http://www.surgeongeneral.gov/library/reports/50-years-of-progress

7. Laws P, Grayson N and Sullivan E. Smoking and pregnancy. AIHW cat. no. PER 33. Sydney: Australian Institute of Health and Welfare National Perinatal Statistics Unit, 2006. Available from: http://www.npsu.unsw.edu.au/NPSUweb.nsf/resources/AMB_2004_2008/$file/Smoking+and+pregnancy+for+web.pdf

8. British Medical Association Board of Science and Education and Tobacco Control Resource Centre. Smoking and reproductive life. The impact of smoking on sexual, reproductive and child health. London: British Medical Association, 2004. Available from: http://www.bma.org.uk/images/smoking_tcm41-21289.pdf

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