Assumptions used in estimating a population benchmark
The assumptions used in estimating a population benchmark for smoking in pregnancy of 0.27%, or 270, per 100,000 population per year is based on the following source(s) of information:
- epidemiological data on the prevalence/incidence of smoking in pregnancy from published research and literature
- activity data to establish smoking in pregnancy from audit and other sources
- current data collection where there is existing national smoking in pregnancy data collection
- additional factors which may influence smoking in pregnancy
- expert clinical opinion of the topic-specific advisory group, based on experience in clinical practice and literature review.
For the purpose of this commissioning guide the population has been defined as women aged 15-44 years old. Approximately 20.5% of the population in England are women aged 15-44 years old.1
The diagram below illustrates four of the stages in pregnancy and the rate of smoking for each stage. For this commissioning guide, the first maternity booking stage has been used as the benchmark rate for the number of women who smoke in pregnancy. This is the expected stage that pregnant women are most likely to be in contact with maternity services. Commissioners should note that higher rates of women who smoke in pregnancy have been reported for the time period before women become pregnant, and in the time period following childbirth.
In the financial year 2008/09 there were around 638,000women who gave birth and had their smoking in pregnancy status recorded.2 It has been calculated that 21.5% of these, or around 131,000 women, would be smoking at first maternity booking. (This is examined further in the ‘current practice' section).
A standard population of 100,000 has around 1,250 pregnancies per year. Of these, 21.5%, or 270 pregnant women, would be smoking at first maternity booking. Currently around 38 pregnant women (14% of the 270) set a quit date with an NHS Stop Smoking Service.
Information gathered from ten local audits on Stop Smoking Services that adopted a routine referral system showed a range of outcomes. The common results include a large increase in the number of referrals to Stop Smoking Services, with an increase in quit dates set and the number of women who successfully quit.
One service adopting such a system estimated that in a 15-month period, almost half of mothers that smoked at first maternity booking set a quit date with the service. In addition, the quit rate for pregnant women accessing Stop Smoking Services increased by 12% during this period.
Another example of a Stop Smoking Service showed that the number of referrals trebled 12 months after a routine referral approach was adopted. There was also around a 50% increase in the number of women setting a quit date.
An increase in the number of referrals of pregnant women who smoke to NHS Stop Smoking Services is likely to have an impact on the number of women that successfully quit. However, commissioners may find that the increase in the number of women who successfully quit is not proportional to the increased number of referrals. This is examined further in the commissioning and benchmarking tool.
It is also likely that there will be additional people taking up the offer of a referral to NHS Stop Smoking Services from partners and others in the households of pregnant women who smoke.
Current data collection
In 2008, the percentage of women who smoked aged 16-44 in Scotland was 29.3%4,5 compared to 26.3%3,6 of women in England aged 16-49. In 2008, the number of women who were smoking in Scotland at first maternity booking was 19.2%.7 The smoking at first maternity booking figure is not currently available for England. However, when taking into account the prevalence of smoking in the two countries, it has been calculated that 17.2% of pregnant women will be smoking at first maternity booking in England.
Current data collection is based on self-reported smoking status. The use of a carbon monoxide (CO) test at first maternity booking to identify pregnant women who smoke is likely to increase the number of pregnant women identified as smoking. Research has shown that self-reported smoking status underestimates the true level of smoking prevalence by 25%.8 When this figure is applied to the number of pregnant women currently identified as smoking at first maternity booking, it increases the number of pregnant women who smoke in England from 17.2% to 21.5%.
For a local population, factors such as deprivation, smoking prevalence and demographics have a significant impact on the number of pregnant women who smoke in pregnancy. The commissioning and benchmarking tool can be used to adjust the national figures to reflect local circumstances.
In 2008/09, the percentage of mothers smoking at time of delivery was 14.4%9 in England. Data shows that there is wide variation among pregnant women who smoke at the time of delivery across primary care trusts (PCTs), ranging from 4.4% to 31.4%.2 The large regional variation reinforces the importance of each PCT gathering local level data in order to accurately calculate the costs that would be incurred and benefits that could be achieved by implementing the guidance.
In 2005, almost four in ten mothers in England (38%) lived in a household where at least one person smoked during their pregnancy.10 In most cases the person who smoked was the mother's partner. Mothers aged 20 or under are five times more likely than those aged 35 and over to have smoked throughout pregnancy (45% and 9% respectively).10 Mothers in routine and manual occupations are more than four times as likely to smoke throughout pregnancy, compared to those in managerial and professional occupations (29% and 7% respectively).10
Expert clinical opinion
In 2008/09, around 19,00011 pregnant women who smoked set a quit date with NHS Stop Smoking Services in England. Of those who set a quit date, 24% were carbon monoxide test validated (CO) at the four-week follow up.11 The consensus opinion of the topic-specific advisory group was that implementing a routine referral service would have an impact on the number of women who set a quit date, and the number of women who successfully quit. In part, the NICE Quitting smoking in pregnancy and following childbirth self assessment tool can be used for data collection to determine the impact of 100% referrals into NHS Stop Smoking Services on the number of pregnant women who set a quit date and who successfully quit.
Based on the epidemiological data and other information sources outlined above, it is concluded that the population benchmark for smoking in pregnancy and referral to an NHS Stop Smoking Service is 0.27% or 270 per 100,000 population per year.
This is based on the following assumptions:
- in 2008/09 there were 637,764 women who gave birth and had their smoking in pregnancy status recorded
- approximately 21.5% of pregnant women will be smoking at first maternity booking
- 100% of pregnant women who smoke will be referred to NHS Stop Smoking Services.
Therefore the population benchmark for smoking in pregnancy and referral to NHS Stop Smoking Services is estimated to be 0.27% per year.
Use the quitting smoking in pregnancy and following childbirth commissioning and benchmarking tool to determine the level of service that might be needed locally and to calculate the cost of commissioning the service using the indicative benchmark and/or your own local data.
1. The Information Centre for health and social care (2010) GP List Populations of Primary Care Organisations
2. Department of Health (2010) Smoking at delivery, GP recorded smoking and GP recorded Obesity (BMI) Quarter 4, 2009/10
3. The Information Centre for health and social care (2009) Health Survey for England - 2008 trend tables
4. National statistics publication for Scotland (2009) Scottish household survey, a survey of the people of Scotland
5. National statistics publication for Scotland (2008) The Scottish Health Survey
6. The Information Centre for health and social care (2009) Health survey for England General Lifestyle Survey 2009
7. ISD Scotland (2010) SMR02 Births and babies, smoking and pregnancy
8. Shipton D, Tappin D, Vadiveloo T et al. (2009) Reliability of self reported smoking status by pregnant women for estimating smoking prevalence: a retrospective, cross sectional study. British Medical Journal 339: b4347
9. The association of public health observatories (2009) Smoking in pregnancy
10. British market research Infant feeding survey 2005. The Information Centre for health and social care (2007)
11. The NHS Information Centre (2009) Statistics on NHS Stop Smoking Services: England, April 2008 to March 2009
This page was last updated: 02 March 2012
- Quitting smoking in pregnancy and following childbirth
- Commissioning services for quitting smoking in pregnancy and following childbirth
- Specifying services for quitting smoking in pregnancy and following childbirth
- Determining local service levels for quitting smoking in pregnancy and following childbirth
- Assumptions used in estimating a population benchmark
- The commissioning and benchmarking tool
- Ensuring corporate and quality assurance