Smoking among pregnant women has declined by 60% to 75% in developed countries. Nevertheless, prenatal smoking remains a common habit with between 10 and 35% of women continuing to smoke throughout their pregnancy, which has an impact on mother and baby before, during and after pregnancy. Before conception, cigarette smoking reduces the changes of conception by reducing fertility in both men and women, reducing zygote implantation and success of infertility treatments.
During pregnancy, smoking accounts for a significant proportion of fetal morbidity and mortality through both a direct (fetal) and indirect (placental) effect. The most important smoking-induced placental pathology is placental abruption with reported risks ranging from 1.4 to 4%. Furthermore, the relationship between maternal smoking and fetal growth is causal, including significant reduction in growth of head circumference, abdominal circumference and especially femur length. Prenatal smoking is associated with a 20% to 30% higher likelihood for stillbirth.
After pregnancy, babies born to smokers weigh on average 200g less than those born to non-smokers; have a 40% increased risk of developing glue-ear, meningitis, chest infection, asthma, breathlessness, and whizzing during childhood. Physical and mental developments have been found to be slower with increasing numbers of studies reporting higher incidence of conduct disorders, behavioral problems, and poorer development in reading and math skills up to age of 16 yrs.
Mechanism of harmful effect
The underlying physiological mechanisms for these ill effects are not fully understood, Many of the 4000 or more chemicals in cigarette smoke are toxic to living cells with the carboxy-haemoglobin causing further tissue hypoxia, further impairing fetal growth and differentiation. Nicotine from cigarette smoke exerts it’s effects indirectly by affecting placental vasculature. After smoking, nicotine is passed from the maternal to the fetal circulation within 15 to 30 minutes with the fetus receiving higher nicotine levels than the mother. Nicotine itself therefore can also cause direct damage by nicotinic acetylcholine receptor binding in fetal membranes causing dysregulation of the nicotinic, muscarinic, catecholaminergic, and serotonergic neurotransmitter systems that are crucial to lung, immune, and neurological development.
Difficulties in quitting
There is a need to encourage women of child-bearing age to quit, if not before pregnancy, then at least as soon as possible after finding out. This is important because research suggests dose most damage and mothers who stop smoking in the first 3 months have virtually identical outcomes to non-smokers.
Women who continue to smoke during pregnancy often feel criticized by society. They may feel guilt and personal conflict at non quitting and many will report to have stopped but continue. Where nicotine levels were routinely taken, 80% of pregnant women who previously smoked had urine and blood levels confirming at least passive smoking- suggesting that self-reports of abstinence are even more inaccurate in pregnancy than in usual stop-smoking clinics.
Pregnancy can be an ideal time to stop smoking, but quitting can be difficult for several reasons. Hysical changes during pregnancy shorten the half-life of nicotine results in an increased desire to smoke. Motivation, which is an essential part of changing health behaviors, is often misplaced and entrancing pressures (such as being told you should quit smoking for your child) have been found to be less influential than intrinsic factors, where there is an expectation or reward or a personal desire to quit for oneself. Indeed, research suggests that expectant mothers who continue to smoke report more skepticism that smoking will harm their baby, than those who quit.
Women most likely to continue smoking throughout their pregnancy are generally of lower age, socio-economic status, level of education, and occupation status. They are likely to come from families where smoking is norm and 80% of those continuing to smoke have a partner who also smokes.
Emphasizing the dangers of smoking alone, without offering specific support, may alienate many addicted young mothers; the lack of many long-term positive outcomes from anti-smoking campaigns may result from ignorance surrounding these socio-economically disadvantaged women’s life circumstances. Many current interventions also ignore the specific psychological stressors and the altered physiological processes that occur during pregnancy. Some authors have claimed that health-care professionals have attempted to manipulate women to stop smoking rather than engage in mutually respectful dialogue.
Smoking cessation in pregnancy
Smoking cessation interventions can be effective in pregnant women but because; less than half of women receive any sort of intervention during their pregnancy, opportunities are missed. Reluctance by the women to utilize available services has been exacerbated by poor referral rates with many midwives admitting a reluctance to bring up the issue of their patient’s smoking.
When the subject of a person’s smoking is not brought up by health professionals it can easily give the impression that it is not important, leading to some ambivalence regarding quitting on the part of the smoker. Failure to discuss the topic also results in many women remaining unaware of the services available to help them quit. Some medical professionals encourage cutting down, but smoking reduction as not been researched in pregnancy.
Pharmacotherapy in pregnancy for smoking cessation
Many prescribers still prefer the woman to try to quit without the use of pharmacotherapy; ’cold-turkey’ appears more possible in women from higher educational backgrounds and social class who are lighter smokers, but the majority of tobacco use in pregnancy is concentrated amongst society’s poorest women.
There is a very little evidence to support the use of the pharmacotherapies that are effective in non-pregnant population. Moreover, we know that nicotine itself has adverse effects on the placenta and fetus, and for the safety reasons it is doubtful that definitive trials investigating the effectiveness of either bupropion varenicline will be conducted in pregnant women in the foreseeable future.
In the short to medium term, information regarding the use of drugs in pregnancy is likely to come from observational studies that are more difficult to interpret than clinical trials. The principal recommendations from these observational pharmacotherapy studies suggest that nicotine replacement therapy (NRT) is safer than smoking in pregnancy. Pregnant women who have unsuccessfully tried to stop without pharmacotherapy should consider using NRT first as this has now been licensed for use in pregnancy. NRT products offering episodic nicotine delivery results in reduced infiltrations to the feetus. For this reason, inhalator, microtabs, lozenge, or gum are recommended but the NRT patch is still the most popular product as it is easy to use, discreet and many pregnant smokers complain the oral products contribute to nausea. Most specialist recommend the 16-h patches to reuse placental/fetal exposure at night.
Dr Efterpi Tingi
Consultant Obstetrician and Gynaecologist
