Smoking, Pregnancy and Fertility

Smoking during pregnancy is the leading modifiable risk factor for poor birth outcomes, including stillbirth, miscarriage, and pre-term birth.^{1 2} Smoking during pregnancy also increases the risk of children developing several respiratory conditions, attention and hyperactivity difficulties, learning difficulties, problems of the ear, nose and throat, obesity, and diabetes.^{1 3 4}

As of 2020/21, 9.5% of women were smoking at the time of delivery, which equates to around 51,000 babies born to pregnant smokers in England each year.⁵ Rates of smoking in pregnancy have a strong social and age gradient with poorer and younger women much more likely to smoke in pregnancy.⁶

In the 2017 Tobacco Control Plan for England, the Government set a target of reducing the prevalence of smoking during pregnancy to less than 6% by 2022, measured as smoking at the time of delivery (SATOD).⁷ However, to achieve this ambition smoking in pregnancy rates would need to decline by 3.5 percentage points by 2022, almost as much as the total decline over the last decade.

This fact sheet reviews the prevalence of, and harm caused by smoking during pregnancy as well as some of the longer-term health risks faced by children born to parents who smoke. It also examines the impact of smoking on fertility.

COVID-19 is a respiratory viral infection that affects the lungs and airways. It is caused by a novel virus called Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2).⁸ This virus has been responsible for millions of infections and deaths worldwide since it emerged in December 2019 and was declared a pandemic in March 2020. ^{9 10}

While data on the link between smoking and COVID-19 is of mixed quality, there is now good evidence to suggest that smoking increases the risk of severe COVID-19 symptoms. A UK study published in January 2021 by researchers from Imperial College London, King’s College London, and the ZOE symptom tracking app suggests that current smokers who get coronavirus are twice as likely to attend hospital and tend to report more symptoms than non-smokers.¹¹ A more recent study published in September 2021 found that current smokers were 80% more likely to be admitted to hospital and significantly more likely to die from COVID-19.¹² The researchers combined genetic data with data from primary care records, COVID-19 test results, hospital admissions data and death certificates.

Similarly, the evidence on the impact of COVID-19 during pregnancy is still developing. At the time of publication there was no data suggesting an increased risk of miscarriage or early pregnancy loss or a problem with the baby’s development in relation to COVID-19.¹³ NHS guidance about pregnancy and coronavirus is available here.

This mixed and developing evidence on smoking and COVID-19 should be put in the context of the proven risks of both smoking and smoking during pregnancy. Smoking damages the heart and lungs and weakens the immune system, making it more likely that smokers will get complications and take longer to recover from illnesses. Pregnant women who smoke are much more likely to experience negative birth outcomes such as stillbirth and miscarriage or contract infections such as pneumonia.^{1 14}

Evidence shows that smoking tobacco, and being exposed to secondhand tobacco smoke, is associated with significantly increased risk of developing respiratory diseases in children and adults.¹⁵ Tobacco smoke weakens the immune system and its capacity to respond to infections which can put you at risk of severe respiratory diseases.¹⁶

For further information see the British Heart Foundation webpage: Does smoking increase or reduce your risk from coronavirus?

Smoking during pregnancy is a health inequality associated with complications in pregnancy, stillbirths, neonatal death and serious long-term health implications for both mothers and their babies.¹⁷ There are big variations in maternal smoking rates, depending on age, geography, socio-economic status, and ethnicity.^{6 18}

Women from disadvantaged backgrounds are more likely to smoke before pregnancy; less likely to quit in pregnancy and, among those who quit, more likely to resume after childbirth.^{19 20} A survey conducted in the UK, reveals 40% of mothers in routine and manual occupations were the most likely to have smoked before or during pregnancy compared to mothers in managerial and professional occupations (14%).²¹ Younger women are also more likely to smoke during pregnancy. In 2017/18, 31% of women aged under 20 were current smokers at their booking appointment compared to just 6% of women over the age of 40.²²

In Scotland 26.6% of pregnant women in the most deprived quintile were smokers at booking, compared to 3.3% in the least disadvantaged group.²³ A similar trend was found in Northern Ireland.²⁴

Pregnant women are also more likely to smoke if they are less educated, live in a community with high smoking rates, single or have a partner that smokes.^{6 20} Women who live with a smoker are six times more likely to smoke throughout pregnancy. Additionally, those who live with a smoker and manage to quit are more likely to relapse once the baby is born.^{21 25}

Smoking during pregnancy, or exposure to second-hand smoke (SHS), restricts oxygen to the baby causing its heart to work faster and exposing it to harmful toxins.²⁶ As a result, it is responsible for an increased rate of stillbirths, miscarriages, low birthweights (babies who are born weighing less than 2,500 grams),²⁷ and birth defects. It also significantly increases the risks of sudden infant death syndrome (SIDS) and adverse health effects in children after birth.^{6 27}

A report published by the Royal College of Physicians in 2010 estimated that in the UK, smoking during pregnancy causes up to 5,000 miscarriages, 300 peri-natal deaths and around 2,200 premature births each year.²⁷ Table 1 shows the increased risk of negative birth outcomes resulting from smoking and exposure to second-hand smoke during pregnancy.

Table 1: Impact of smoking and exposure to secondhand smoke during pregnancy

^{Source: Zhao L et al. Parental smoking and the risk of congenital heart defects in offspring: An updated meta-analysis of observational studies. 2020; RCP. Hiding in plain sight: treating tobacco dependency in the NHS. 2018; Pineless BL et al. Systematic review and meta-analysis of miscarriage and maternal exposure to tobacco smoke during pregnancy. 2014; RCP & RCPCH. Passive Smoking and Children. 2010}

Compared to 2017/18, it is estimated that if the Government’s ambition to reduce rates of smoking in pregnancy to 6% or less by 2022 is realised, it will result in:²⁸

• 45 – 73 fewer stillbirths
• 11 – 25 fewer neonatal deaths
• 482 - 766 fewer preterm births
• 1455 – 2407 fewer babies born at low birth weight.
• 7 – 11 fewer sudden infant deaths

Foetal Growth and Birth Weight
Maternal smoking during pregnancy is known to be associated with intrauterine growth restriction which can result in low birth weights and babies who are small for their gestational age (SGA).^{27 29} Available evidence has shown that smoking during pregnancy can lead to growth reduction of the foetal head and smaller head circumference at the time of birth.^{30 31} Babies born to mothers who smoked have been found to weigh an average of 250 grams less compared to those born to non-smokers.²⁷

Miscarriage, Stillbirth, and Preterm Birth
The risks of miscarriage, perinatal mortality (stillbirth and neonatal death) and preterm birth are all linked to smoking during pregnancy.²⁷

Miscarriage, also known as spontaneous abortion, is one of the most common adverse pregnancy outcomes. It usually occurs during the first 24 weeks of pregnancy as a result of chromosomal abnormalities, hormonal problems, lifestyle and environmental factors.³² Smoking during pregnancy has been found to increase the risk of miscarriage by 24-32%.²⁷ A systematic review published in 2014 found that there is a dose respondent relationship between the number of cigarettes smoked and the risk of miscarriage, with a 1% increase in relative risk of miscarriage per cigarette smoked per day.³³ Secondhand smoke exposure during pregnancy was found to increase the risk of miscarriage by 11%.³³

Perinatal mortality includes stillbirth, where a baby is born dead after 24 completed weeks of pregnancy, and neonatal death, the death of a baby within the first four weeks of being born.³⁴ In 2010 it was estimated that maternal smoking causes 300 perinatal deaths in the UK each year.²⁷ A systematic review published in 2015 found that women who smoke during pregnancy have a 47% increased risk of stillbirth and that the risk of death increases with the amount smoked during pregnancy.²⁶

Preterm birth (birth of a baby born before 37 weeks gestational age) continues to be the biggest cause of neonatal mortality and morbidity in the UK, with neurodevelopmental disability being one of the major long- term consequences.³⁵ Maternal smoking increases the risk of preterm birth and in 2010 it was estimated that smoking was responsible for 2,200 premature singleton births in the UK each year.²⁷ Similarly, a study from Sweden found that heavy smoking during pregnancy increased the risk of having an extremely preterm baby (born before 28 weeks gestation) by 91%.³⁶ The association between smoking and preterm birth was stronger for earlier-term births.³⁶

Exposure to tobacco smoke during pregnancy negatively impacts offspring from infancy to childhood and into adulthood.²⁷

Sudden Infant Death Syndrome
Maternal smoking during pregnancy and post-natal exposure to tobacco smoke is a major risk factor associated with sudden infant death syndrome (SIDS), also known as cot death.^{27 37}

Research has established that babies whose mothers smoke are up to 3 times more likely to die from sudden infant death, compared with babies whose mothers do not smoke.²⁷ Additionally, infants (children less than 1 year) who co-sleep with mothers that smoke have been found to be at an elevated risk of cot death.³⁸ A study published in 2019 found that maternal smoking during any trimester more than doubles the risk of sudden infant death.³⁹ However, mothers that reduced the number of cigarettes smoked or decided to quit decreased the risk of SIDS compared to mothers who continued smoking.³⁹

To help reduce the risk of cot death it is highly recommended that all parents maintain a smokefree home.⁴⁰ Since October 2015, it has been illegal to smoke in a private car carrying someone under the age of 18.⁴¹

Asthma and Respiratory Infections
Infants and children of parents who smoke are twice as likely to suffer from a serious respiratory infection as the children of non-smokers.²⁷ Smoking during pregnancy can also increase the risk of asthma and wheezing in young children and adolescents.^{42 43} Research suggests that the increased risk of asthma and respiratory infections may be due to changes in biological receptors in the baby’s immune system that are responsible for recognising and fighting infections and bacteria.⁴⁴ Smoking during pregnancy is also associated with an increased risk of infantile colic.^{45 46}

Early developmental exposure to cigarette smoke can result in epigenetic changes – which alter the structure of genes - in the lungs of the offspring which can be transferred to the following generations, resulting in adult-onset of respiratory disease.⁴⁷ Some evidence shows an association between maternal smoking, early childhood exposure to second-hand smoke and the development of emphysema in adulthood. The findings suggest that the lungs may not recover completely from the effects of early-life exposure.^{48 49}

Meningitis
Evidence shows that maternal smoking appears to more than double the risk of bacterial forms of meningitis, such as meningococcal meningitis.^{27 50}Low birth weight and premature birth – both of which are associated with maternal smoking – are also risk factors for meningococcal disease.⁵⁰

A 2012 metanalysis study found that secondhand smoke exposure in the home doubled the risk of invasive meningococcal disease, with some evidence of an exposure–response gradient. This effect was strongest in children under 5 years and in children whose mothers smoked during pregnancy.⁵¹

High Cholesterol and Obesity (Start)
A 27-year study examining cholesterol in children found evidence suggesting that maternal smoking in pregnancy is associated with an increased rise in total cholesterol levels and a tendency towards an adverse lipoprotein profile in the offspring.⁵²

Another study concluded that smoking among pregnant women is independently associated with significantly lower high-density lipoprotein cholesterol in healthy 8-year-olds.⁵³ Adults who were small for gestational age at birth as a result of maternal smoking also have an increased risk of hypercholesterolemia (high cholesterol).⁵⁴ An additional study conducted among school children aged 9 and 10 years found that Body Mass Index (BMI) and Obesity Index (OI) were higher in children whose mothers smoked during pregnancy. And the degree of elevation was positively correlated with the duration of maternal smoking.⁵⁵

There is strong evidence that childhood overweight and obesity can be related to smoking during pregnancy.^{56 57 58} Two meta-analyses of 7 and 14 studies respectively found that, for children of mothers who smoked during pregnancy, there was a 47-50% increase in the odds of being overweight in childhood.^{59 60}

Childhood Cancer
Maternal smoking during pregnancy is also linked with an increased risk of childhood cancer.⁶¹ The association with lymphoma was seen in a case-control study published in 1986, researchers observed a dose-response relationship between the number of cigarettes smoked per day by the mother during pregnancy and cancer risk in offspring. Compared to a control group the risk for the experimental group was doubled for non-Hodgkin lymphoma, acute lymphoblastic leukaemia, and Wilms' tumour.⁶²

A 2016 metanalysis study also found increased risks of brain and central nervous system tumours and even lymphoma, predominantly non-Hodgkin lymphoma in children of mothers who smoked during pregnancy.⁶³ Another study suggests maternal smoking during pregnancy maybe a risk factor for retinoblastoma (retinal cancer) and certain types of childhood brain tumours.⁶⁴

Offspring Fertility
Research suggests that maternal smoking may have a negative impact on the fertility of both male and female offspring.^{65 66 67} Smoking during pregnancy reduces the number of germ cells that form in the developing foetus.⁶⁸ In males it has an impact on protamine, a protein essential in sperm production which can lead to fertility problems.⁶⁹ Other studies further show that men whose mothers smoked while pregnant are at risk of having smaller testes,⁷⁰ lower mean sperm concentration and lower total sperm counts.⁷¹

Other Adverse Health Impacts
Further impacts of smoking during pregnancy include:

• Increased risk of congenital defects in the offspring of smokers,⁷² including orofacial clefts;^{73 74} neural tube defects (defects of the defects of the brain, spine, or spinal cord)^{75 76}; cardiovascular/heart defects, musculoskeletal and other defects.⁷³
  
• Potential adverse implications for the long-term physical growth and intellectual development of the child.^{77 78}
• Researchers have also found that adults exposed to tobacco smoke in utero had a more adverse cardiovascular disease risk profile.⁷⁹ There is even evidence that prenatal and postnatal second-hand smoke contributes to insulin resistance in children.⁸⁰
• Maternal smoking has been associated with an increased risk of learning difficulties.⁸¹ Available evidence has established that smoking during pregnancy increases foetal testosterone levels⁸² which have been associated with an increased risk for autism,⁸³ and antisocial disorder later in life.⁸⁴ Numerous studies have also demonstrated a link between maternal smoking and ADHD,^{3 85 86} as well as new research linking second-hand smoke and ADHD.⁸⁷
• Studies have found that maternal smoking is associated with increased conduct problems and
  externalising, aggressive and overactive behaviour in children.^{88 89} Smoking during pregnancy and
  exposure to secondhand smoke in early childhood have been found to be “quite strong” predictors of
  anti-social behaviour and crime later in life.^{90 91 92} This finding is supported by other studies exploring
  the relationship between maternal smoking during pregnancy and behaviour problems in childhood
  and adolescence,^{88 93 94} including smoking (particularly among girls)^{95 96} and other substance use.^{97 98 99}
• A population-level study of children in Finland found that the risk of psychiatric morbidity was significantly higher in the children of mothers who smoked during pregnancy.¹⁰⁰ A follow-up study found that this was still the case even when genetic and familiar factors are thoroughly controlled.¹⁰¹
• Some evidence suggests that prenatal exposure to tobacco smoke may be associated with benign breast disease later in life.¹⁰²
  

Tobacco smoke contains over 7,000 chemical compounds, many of which can cause cancer ¹⁰³ and dozens of which are known or suspected reproductive toxins.¹⁰⁴ Consequently, exposure to secondhand smoke before and during pregnancy can lead to many of the same adverse birth outcomes experienced by women who smoke, including difficulty becoming pregnant in the first place.

Low Birth Weight and Preterm Birth
Non-smoking women exposed to other people’s tobacco smoke during pregnancy are more likely to have lower-weight babies.^{1 105 106} On average, infants born to mothers exposed to secondhand smoke during pregnancy are 30-40g lighter than infants born to women who have not been exposed.²⁷Low birth weight (LBW) is associated with adverse health and developmental outcomes.¹⁰⁷Exposure to secondhand smoke has also been significantly associated with a greater risk of preterm birth.¹⁰⁸

Perinatal Mortality and Congenital Malformations
Exposure to secondhand smoke during pregnancy is associated with a higher risk of stillbirth,^{109 110} spontaneous abortion¹¹¹ and of having a baby with congenital malformations.¹⁰⁴

Leukaemia
Some studies show evidence of prenatal and postnatal secondhand smoke potentially having a causal relationship with leukaemia,^{112 113} particularly acute lymphoblastic leukaemia.¹¹⁴A study conducted in Australia found that paternal smoking around the time of conception increased risk factor of acute lymphoblastic leukaemia in children by 15%.¹¹⁴The risk increased to 44% in children whose fathers smoked more than 20 cigarettes per day at the time of conception.¹¹⁴

Fertility and Reproduction (See Fertility section below)
Evidence also suggests that smoking and secondhand smoke exposure damages female fertility and can make it harder for women to conceive¹¹⁵ (see fertility section below).

Pregnancy is a “teachable moment”, and evidence has shown that more women quit smoking when they are pregnant than at any other time during their lives.¹¹⁶ One study found that pregnant smokers were twice as likely to attempt to quit smoking as non-pregnant women.¹¹⁷ Many women mange to quit smoking during pregnancy without support, although this may make the risk of postpartum relapse greater.¹¹⁸

Smoking cessation interventions have been shown to reduce the number of newborns with low birth weight and preterm births.¹¹⁹ In one study, compared to ongoing heavy smoking, quitting was associated with a 299g increase in birth weight, while the babies of light smokers who quit entirely saw a 63g increase in birth weight.¹²⁰

National Guidance
In England, reducing stillbirths and neonatal deaths is a national priority.¹²¹ The National Institute for Health and Care Excellence (NICE) has published guidance to on supporting pregnant smokers to quit during pregnancy and after childbirth¹²² and on the support that should be provided by maternity services.¹²³ Among the recommendations are that all women should be monitored for carbon monoxide exposure (a marker for smoking) and asked about their smoking status at their maternity booking appointment, with smokers referred to specialist stop smoking support.¹²³

In 2016, the NHS launched the Saving Babies’ Lives Care Bundle (SBLCB)¹²⁴ as part of measures designed to halve rates of stillbirth and neonatal death by 2025, with an updated Version 2 published in 2019.^{125 126} ‘Element 1: Reducing smoking in pregnancy’ recommends carbon monoxide (CO) testing of all pregnant women at the antenatal booking appointment; CO testing a 36 weeks; referral to a stop smoking service/specialist based on an opt out system; and training on CO monitor use and Very Brief Advice (VBA) for all relevant maternity staff.

The NHS Long Term Plan, published in 2019, includes a commitment to deliver an opt-out smokefree pregnancy pathway including focused sessions and treatments for expectant mothers and their partners.”¹²⁷ This support will complement, rather than substitute, existing local authority-funded stop smoking services. Approximately 43% of NHS trusts surveyed by ASH in 2020 reported commissioning specialist stop smoking support for pregnant women in 2020/21.¹²⁸

Nicotine Replacement Therapy
Pregnant women who are trying to quit smoking should be supported to use nicotine replacement therapy (NRT) to help them manage nicotine withdrawal and stay smokefree. A review of the efficacy and safety of NRT in pregnancy found that NRT increased smoking cessation rates, measured in late pregnancy, by approximately 40%.¹²⁹ The authors found no evidence that NRT used for smoking cessation in pregnancy has either positive or negative impacts on birth outcomes.

Another study found that NRT use significantly decreased the risk of preterm delivery and low birth weight compared to smokers and found that NRT use does not appear to increase the risk of malformations.¹³⁰ Since NRT is metabolised faster during pregnancy, pregnant women may need higher doses of NRT in order to alleviate cravings.¹³¹ Additional research is needed on which types and doses of NRT are the most effective in helping pregnant smokers quit, while also protecting the foetus.¹²⁹

Currently, the National Institute for Health and Care Excellence (NICE) recommends the use of NRT by pregnant women only if they have been unable to quit without NRT, recognising that NRT is a reduced risk way of using nicotine compared to smoking, but is unlikely to be without risk. NICE does not recommend the use of either bupropion or varenicline by pregnant or breastfeeding women.¹²²

Behavioural Support
Behavioural support involves scheduled meetings in which people who smoke receive information, brief advice, encouragement, and some form of behavioural intervention – motivational interviewing or cognitive behavioural therapy.^{1 132}In the UK, this therapy is offered weekly for at least the first 4 weeks of a quit attempt that is, for 4 weeks following the quit date.¹³²

Evidence has shown that behavioural support is effective in increasing quit rates.¹³³ However, a Cochrane review found that compared with usual care, a combination of behavioural interventions as an adjunct to NRT increased the chance of success by about 10% to 20%.¹³⁴

Financial Incentives
Evidence shows that financial incentive schemes designed to support women to quit smoking during pregnancy are effective in increasing quit rates when coupled with evidence-based support in line with NICE Guidance.¹³⁵ A 2017 Cochrane review found psychosocial interventions which involve counselling, feedback and incentives increased the proportion of women who had stopped smoking in late pregnancy. However, the characteristics and context of the interventions should be carefully considered before implementing it in your setting.¹⁷

The latest Cochrane Review of the evidence on the use of financial incentives for smoking cessation found that women receiving incentives were more than twice as likely to quit and remain quit postpartum compared to women receiving usual care without incentives.¹³⁶

Evidence shows incentive schemes are also cost-effective. A UK study which involved over 600 women from Glasgow assessed the cost-effectiveness of offering up to £400 of shopping vouchers in addition to routine care. The evaluation was undertaken from the UK NHS perspective for the cost year 2013, with results showing that the incremental cost per quitter at 34-38 weeks pregnant was £1127. The lifetime model resulted in a longer-term cost of £482 for each quality-adjusted life-year gained (£482/QALY). This is well below the NICE cost-effectiveness threshold of £20,000 per QALY.¹³⁷

Whole Family Approach: Engaging Women's Partners
The NHS Long Term Plan’s commitment to include pregnant women’s partners in the tobacco dependence treatment pathway recognises that women’s environments have a crucial impact on their smoking.¹²⁷

Evidence suggests that over three-quarters of women who quit smoking during pregnancy relapse post- partum, and this period should continue to be a focus for providing support to new mothers.^{118 138} One way pregnant women can get support is through initiatives to make homes smokefree, thus protecting all family members from smoke exposure and reducing the chances of relapse. Several studies conducted in the UK reveal that adjusting to a new maternal identity as a non-smoker can be a major challenge for women who quit smoking during pregnancy.^{139 140} However, women may be more likely to successfully quit smoking if partners and other household members who smoke are also supported to stop smoking.

Evidence from a pilot in Dorset, where specialist smoking midwives provide pharmacotherapy and combined behavioural counselling sessions to both pregnant smoker and smoking partners/family members for the duration of the 12-week programme show that these kind of interventions are effective in engaging pregnant smokers and increase quit rates.¹⁴¹ The findings reveal pregnant womens’ quit rate increased from 75% to 82% while partner engagement rate increased from 4% to 39% and partner quit rates increased from 2.2% to 60%.¹⁴¹This indicates that interventions which are delivered at the household level can be effective for engaging smoking partners, as they frame smoking as a household responsibility, with family-wide impact. Partners need to be involved not just as providers of social support but as participants with a stake in the change process.¹⁴²

E-cigarettes and Pregnancy
Electronic cigarettes (e-cigarettes) are currently the most popular aid to quitting smoking in England.¹⁴³ Evidence shows that e-cigarettes are considerably less harmful than smoking, though not completely risk free.^{144 145} According to the findings of a recent Cochrane review, nicotine-containing e-cigarettes are approximately 70% more effective in supporting smokers to quit successfully than NRT.¹⁴⁶

Little research exists regarding the safety of using e-cigarettes during pregnancy, however evidence from adult smokers in general suggests that they are likely to be significantly less harmful to a pregnant woman and her baby than continuing to smoke. More research is needed in this area. As in other populations, pregnant women who use e-cigarettes are likely to do so to stop smoking.¹⁴⁷ While licensed Nicotine Replacement Therapy (NRT) products such as nicotine patches, gum and inhalers are the recommended option, if a pregnant woman chooses to use an e-cigarette to help her quit smoking or stay smokefree, she should be supported to do so.¹⁴⁸

See also: Smoking in Pregnancy Challenge Group information on Using e-cigarettes before, during and after pregnancy

The Smoking in Pregnancy Challenge Group is a coalition of organisations committed to reducing rates of smoking in pregnancy. The Group is a partnership between the Royal College of Midwives, the Royal College of Obstetricians and Gynaecologists and the Royal College of Paediatrics and Child Health, the voluntary sector and academia.¹⁴⁹ The Challenge Group has produced several reports reviewing the progress made in reducing smoking in pregnancy in England, including the most recent: Getting back on track: Delivering a smokefree start for every child in 2021.¹⁵⁰

Challenge Group resources and information can be accessed here.

Smoking negatively impacts the ability to conceive for both men and women.¹⁵¹ Toxicants from smoking affect gametes, hormone regulation and reproductive organs reducing the chance of, or delaying conception.¹⁵² Smoking during pregnancy also has negative implications for the offspring’s fertility later in life.¹⁰⁴

A literature review examining the relationship between smoking and fertility concluded that tobacco use affects every system involved in the reproductive process.¹⁵³ This is supported by a systematic literature review which found that “all stages of reproductive functions are targets of cigarette smoke toxicants.”¹⁵⁴

Female Fertility
Many factors, including smoking, influence a woman’s ability to conceive and have a healthy baby.^{155 156} Specifically, smoking affects uterine receptivity. Uterine or endometrial receptivity is the ability of the uterus to allow embryos to implant with the quantity of tobacco smoked is negatively correlated with the level of uterine receptivity.¹⁵⁷ However, there is no safe level of smoking, and even comparatively low levels of smoking can have a significant impact on female fertility. Cotinine, a by-product of nicotine, can damage fallopian tubes through altering gene expression.¹⁵⁸

There is also evidence that women who were ever-smokers during their reproductive years had greater estimates of risk of tubal ectopic pregnancy.^{111 116} This was also evident among never-smoking women with the highest levels of lifetime exposure to secondhand smoke.^{111 158}

Smokers have been found to have both shorter and more variable menstrual cycle lengths than non-smokers which can affect fertility.¹⁵⁹ More variable cycle lengths can impact on fertility as the timing of ovulation is less predictable. Smokers tend to have shorter cycles compared to non-smokers, which are specifically shorter in the follicular phase, indicating abnormalities in ova maturation. These abnormalities lead to a reduced chance of successful conception.¹⁵⁵ Smokers also have a tendency to have shorter menstrual cycling lifespans – meaning they are likely to enter the menopause earlier than non-smokers, reducing their reproductive lifespan.^{160 161}

There is evidence to suggest that smoking reduces the success rates of fertility treatment. Studies of women undergoing assisted reproductive treatment have demonstrated a significant negative effect associated with smoking.^{115 162}One study of 499 women seeking IVF treatment found a 50% reduction in implantation rate among smokers compared to women who had never smoked.¹⁶³

Oral Contraception
Women who use combined oral contraceptives are at increased risk of heart disease;¹⁶⁴because the risk of heart disease in young women is low, the benefits of using the pill generally outweigh the risks for young women who do not smoke. Pill-users who smoke are also at risk of venous thromboembolism and arterial thrombosis (blood clots in the veins and arteries).^{165 166} It is therefore important that all women who take the contraceptive pill be advised not to smoke.

Menopause
Smoking is associated with early onset of menopause.^{167 168} The likelihood of earlier menopause is related to the number of cigarettes smoked; with those smoking more than ten cigarettes a day have an increased risk of early menopause.¹⁶⁹

A recent study conducted in the United States of America found that there is an association between smoking, infertility, and early onset menopause.¹⁷⁰Women who had never smoked but exposed to a lifetime of passive smoke had an increased risk of infertility, and they were more likely to reach menopause 13 months earlier compared to non-smokers and those not exposed to passive smoke.¹⁷⁰ This was also evident among active smokers, as they were more likely to reach menopause almost 22 months earlier than never smoked women.¹⁷⁰

Stopping smoking may lower the risk of early menopause. While current smokers’ risk of early menopause is twice that of non-smokers, in ex-smokers, the risk is higher by just one-third. Research suggests that polycyclic aromatic hydrocarbons found in tobacco smoke can trigger premature egg cell death which may, in turn, lead to earlier menopause.¹⁷¹Another study suggests that chemicals in tobacco smoke alter endocrine function, which in turn affects the release of pituitary hormones. This endocrine disruption is thought to contribute to adverse outcomes, including earlier menopause.¹⁷²

Male Fertility & Sexual Impotence
A range of studies have demonstrated the negative impact of smoking on male sex cells. There is a significant association between smoking and sexual impotence, with the association increasing with the number of cigarettes smoked per day.^{173 174}

There is a correlation between the number of cigarettes smoked and the damage to sperm, and researchers have found that any level of smoking is associated with reduced male fertility.^{67 155} Compared to non-smokers, smokers typically have lower semen volume, lower sperm count and reduced sperm motility¹⁷⁵ all of which reduce the chances of successful conception. Specifically, by-products of nicotine reduce the motility of sperm and their fertilization capacity.^{176 177}

Sperm from smokers specifically have a reduced fertilization capacity in the form of lower acrosin activity. Acrosin is the digestive enzyme that aids in the penetration of ova.¹⁷⁵ Smoking causes DNA fragmentation which prevents successful activation of acrosin, therefore preventing fertilisation of ova.¹⁷⁵

Male smokers have an increased risk of erectile dysfunction as chemicals from cigarette smoke damage arteries affecting the blood supply to the penis.¹⁷⁸