Introduction to smoking during pregnancy
Many women are exposed to tobacco smoke before or duringpregnancy, either because they smoke cigarettes, or because they inhale cigarette smoke from their environment (e.g. in a house where their partner is smoking). Smoking or being exposed to tobacco smoke, either before or during pregnancy is associated with a range of poor pregnancy outcomes, including reduced fertility, an increased risk of pregnancy complications and impaired infant and child development. Tobacco smoke exposure is considered one of the few, preventable causes of poor pregnancy outcomes in developed countries like Australia.
Prevalence of tobacco use during pregnancy
Around 17% of Australian women smoke whilst pregnant.
Health impact of smoking on pregnancy
Tobacco smoke contains a number of carcinogens (agents which cause cancer). The carcinogens in tobacco smoke have been shown to accumulate in and damage almost all body organs, including the reproductive organs. Smoking also alters the chemical environment of the smoker’s body while they are consuming tobacco products (e.g. lowers oxygen supply). Thus, smoking can affect a woman’s chances of experiencing a healthy pregnancy even before she conceives, as smoking reduces her chance of becoming pregnant.
There is also strong evidence that exposure to tobacco smoke during pregnancy negatively affects pregnancy outcomes. When a pregnant woman is exposed to tobacco smoke, either from her own, or another person’s cigarette, her foetus is also exposed. There is strong evidence that such exposure is harmful for the foetus, both in the immediate and long term. In the short term, foetal tobacco exposure increases the risk of pregnancy complications (e.g. premature birth) and impairs foetal growth. In the long term, infants born to women who smoked during pregnancy have higher rates of infant and childhood illness and death. The more a woman smokes, the greater the risk of poor pregnancy, infant or childhood health outcomes.
Women who smoke are more likely to be infertile than their non-smoking counterparts. Collectively, 12 studies examining the association between smoking and female infertility in European and other countries reported that female smokers were >60% more likely to be infertile than non-smokers. Australian studies show that females who smoke double their risk of infertility compared to those who do not smoke.
Studies have also shown that smoking affects a woman’s menstrual cycle in ways which reduce fertility. Women who smoke, on average, are more likely to experience irregularmenstrual cycles, amenorrhoea and early menopause than women who do not smoke.
Response to in vitro fertilisation
Many infertile women are able to conceive through in vitro fertilisation. However, women who smoke are less likely to become pregnant after an IVF embryo is transferred into their uterus, than women who do not smoke. Evidence from nine studies of the effects of smoking on in vitro fertilisation outcomes showed that the smokers were 34% less likely to become pregnant after IVF treatment than non-smokers. Evidence suggests that the toxins in cigarette smoke negatively affect the ability of an embryo (a fertilised egg) to implant into the lining of the uterus and form a pregnancy. If the embryo does successfully implant, the toxins in cigarette smoke may also affect the embryo’s growth in the very early stages of pregnancy.
A woman’s tobacco smoke exposure during pregnancy affects the development of her foetus from the very early stages of pregnancy and increases the likelihood that she will experience complications during pregnancy.
Australian research shows that women who smoke during pregnancy are 36% more likely to have a miscarriagethan those who do not smoke. Some 9% of miscarriages could be prevented by preventing pregnant women from smoking.
Australian studies show that smoking during pregnancy increases the risk ofectopic (extra-uterine or tubal) pregnancy by 46% and that 11% of ectopic pregnancy cases in Australia are caused by smoking. A study from France showed that the more a woman smoked, the more likely she was to have an ectopic pregnancy. In that study women who smoked >20 cigarettes per day were 3.9 times more likely, and those who smoke <10 cigarettes per day being only 1.7 times more likely to experience ectopic pregnancy than those who had never smoked.
In Australia, infants born to smoking women in 2003 were 60% more likely to bedelivered preterm than infants born to non-smoking women.
Premature rupture of membranes, placenta praevia and placental abruption
Research has shown that Australian women who smoke are almost twice as likely to experience premature rupture of the membranes (their water breaking prematurely, before they are in labour). Some 21% of cases of premature rupture result from smoking. Smoking during pregnancy also increases the risk of placenta praevia.
In addition, women who smoke during pregnancy are more likely to experience placental abruption than those who don’t smoke. The risk of placental abruption is highest in heavy smokers, who are twice as likely to experience placental abruption compared to women who do not smoke during pregnancy.
Intrauterine growth retardation and low birth weight
Intrauterine growth retardation, a condition in which the foetus does not grow as much as it should throughout the pregnancy, typically results in low birth weight (a baby born weighing <2.5kg). It is associated with numerous infant, childhood and adolescent health problems. Smoking interferes with the growth of the foetus in utero and thus increases the likelihood of intrauterine growth retardation and the infant being delivered at a low birth weight.
The foetuses of smoking women are, on average, 200g lighter than those of non-smoking women. The more a woman smokes the lighter her infant is likely to be, and women who smoke heavily may bear infants up to 500g lighter than average weight babies. In Australia, female smokers are twice as likely to deliver a low birth weight baby than non smokers.
Passive smoking during pregnancy also increases the risk of intrauterine growth retardation and low birth weight. One very large study reported that passive smoking during pregnancy increased the risk of delivering a low weight baby by 32%.
Smoking during pregnancy is also associated with poor health outcomes after childbirth, in the infants and children born to smoking mothers.
Australian studies show that women who smoke during pregnancy are 33% more likely to bear a stillborn infant. Some 9% of stillbirths in Australia result from smoking.
Early infant death
There is strong evidence that a woman smoking during pregnancy increases her infant’s risk of death in the first four weeks of its life. Australian studies show that infants born to women who smoked during pregnancy are 28% more likely to die within 28 days of birth than infants born to women who did not smoke during pregnancy. Data from other developed countries has also show an increased risk of early death in the infants of women who smoke.
Sudden infant death syndrome (SIDS)
Infants born to mothers who smoke during pregnancy are up to 3 times more likely to die from SIDS than those born to non smoking women. Australian evidence shows a 2.7 times increased risk of SIDS in smokers’ infants, and that 34% of all SIDS cases result from smoking. SIDS is also more common in babies whose parents smoke after childbirth.
Childhood respiratory illnesses including asthma
Smoking during pregnancy increases the risk of a number of childhood respiratory illnesses, even if the child’s parents do not smoke during the first two years of its life. One study reported that 6-12 year old children born to smokers were 25% more likely to wheeze, 18% more likely to have asthma and 13% more likely to cough at night, than infants born to non-smoking parents.
Recently evidence has emerged that there is an association between smoking during pregnancy and digital anomaly (incorrect number of fingers or toes) in the infant. There is no evidence that other congenitalabnormalities (e.g. spina bifida) are associated with smoking.
Quitting smoking during pregnancy
Many women may decide to quit smoking when they find out they are pregnant. Women who are trying to fall pregnant should ideally quit smoking prior to conception. A significant proportion of Australian women (25-40%) quit smoking spontaneously when they discover they are pregnant, however others find quitting more challenging and may benefit from professional assistance. Many healthcare professionals are able to provide assistance to women who wish to quit smoking, for example by referring them to quit smoking programs, support groups or prescribing medications to assist them in quitting smoking. Evidence shows that women who attend quit smoking programs are more likely to stop smoking while they are pregnant.
It is also important that pregnant women with smoking partners are aware of the adverse effects of their partner’s smoking, and develop strategies to reduce their exposure to their partner’s tobacco smoke. For example the woman’s partner should not to smoke in the house or close to her.
The benefits of quitting
Quitting smoking early in pregnancy reduces the risk of many of the poor maternal and infant outcomes outlined above. For example, a woman who quits smoking during the first trimester of pregnancy is likely to bear an infant of equivalent weight to a woman who never smoked during pregnancy.
Pregnant women and those planning a pregnancy should also be aware of other factors which can affect foetal health during pregnancy, including:
- good nutrition;
- regular exercise;
- abstaining from or reducing alcohol consumption; and
- reducing stress.
Nicotine Replacement Therapy (NRT)
Nicotine replacement therapy (NRT) has been used as a successful intervention for quitting smoking for more than 20 years. Research has indicated NRT can increase the long-term quit rate by 50-70%. As the name suggests, NRT “replaces” nicotine into the bloodstream which is lost when the smoker attempts to quit and has stopped smoking, but without the many thousands of chemicals which are consumed when smoked and are responsible for tobacco related diseases. For this reason, NRT has been thought of as ‘clean nicotine’.
NRT is an efficacious tool for smoking cessation although its safety and efficacy in pregnancy and birth outcomes has not been established. That said, we must keep in mind that the ultimate goal during pregnancy should be to avoid nicotine and tobacco and therefore it is believed that the benefits of tobacco cessation during pregnancy outweigh the risks of using NRT compared to those if the women continued to smoke. While nicotine may be toxic to the foetus, the level of nicotine is reduced and exposure to the other toxic chemicals in cigarettes is avoided with NRT.
In Australia, clinical guidelines recommend the use of NRT in pregnant women who are otherwise unable to quit smoking and psychological interventions have failed.
NRT use in pregnancy must be under the strict recommendation and guidelines of your doctor.
More information on NRT use in pregnancy
|For more information about pregnancy, including preconception advice, stages of pregnancy, investigations, complications, living with pregnancy and birth, see Pregnancy.|
|For more information about pregnancy planning, including importance of nutrition before pregnancy, being under-weight, being overweight, tobacco exposure and alcohol consumption,see Pregnancy Planning (Preconception Advice).|
|For more information on smoking and its health effects, and some useful tools, videos and animations, see Smoking|