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A Framework for maternity services in Scotland

Appendix 4

Estimating future numbers of births in Scotland

Acknowledgements

This report has been provided by Dr Margaret Douglas, Consultant in Public Health Medicine, Lothian Health Board. Dr Douglas acknowledges with thanks the assistance provided by Graham Jackson and Garnett Compton of the General Register Office for Scotland, who provided data and discussed the analyses, Chris Shaw of the Government Actuary's Department who carried out projections, and Dr Jim Chalmers of ISD who discussed the analyses and implications.

Figure 1 shows the total number of births in Scotland, from 1974 to 1999. Over the 1990s, the number of births has fallen, from 67,000 in 1991 to 55,147 in 1999. In order to plan maternity services, it is essential to know if this trend is likely to continue.

Figure 1 Total number of births in Scotland, 1974-1999

Source GROS

The following sections attempt to predict the numbers of births that may be expected in Scotland, and in each Health Board area of Scotland, in each year to 2010.

What influences the number of births?

The number of births in any given year depends on two things: the number of women of reproductive age, and their fertility rates.

Women of reproductive age

The women who will be in the reproductive age group in 2010 have already been born. Mortality rates in these age groups are low, and are fairly stable. So it is possible to project the number of women of each age to 2010 and to be confident of the results. The main uncertainty relates to future trends in migration of women into or out of Scotland.

Figure 2 shows that the total number of women of reproductive age is projected to fall from 1,090,000 in 1998 to 994,000 in 2010. More detailed examination of the projections in different age groups is shown in Table 6. This suggests that the number of women aged 20-24 years will increase, but there will be marked declines in the populations of women aged 25-39 years. This is because the current population at these ages is swelled by the 'baby boom' generation. It is important when predicting overall birth rates, because peak fertility now occurs in women of these ages.

Figure 2 Projected total number of women aged 15-44 years, 1998-2016

Source: GROS

Fertility rates

The fertility rate in Scotland has been declining since a peak in the 'baby boom' years of the 1960s. The summary measure of fertility is the Total Fertility Rate, defined as the average number of children a woman would have if she lived to at least the age of 44 years and experienced the present age specific fertility rates at every age. The Total Fertility Rate declined from 3.00 in 1965 to 1.51 in 1999.

Table 6 Total number of women in each reproductive age group, in thousands, 1998-2011

Source GROS

Figure 3 shows the trend in age specific fertility rates in Scotland, from 1965 to 1999. It shows that, over that time, the fertility rates declined at all ages, and the peak age of childbearing became older. In the 1960s the highest fertility rates were in women aged 24 years, whereas women of around 30 years experience the highest fertility now. This means that, among women in their 30s and 40s, fertility rates are starting to increase, although they are still lower than the rates observed in women of those age groups in the 1960s.

Figure 3 Age specific fertility rates, 1960-1999

Source: GROS

Cohort and period fertility

Fertility rates measured over a calendar year are called 'period' rates, and can be misleading if the pattern of childbearing is changing. If women are delaying childbearing to older ages, period rates can give a false impression. Period rates are also very sensitive to short term economic changes, which may alter the timing of births but not the overall number of children that families have. For this reason, it is often more meaningful to calculate the average completed family size for a birth cohort of women.

True changes in fertility across the reproductive lifespan can be seen by comparing the fertility experience of women in different birth cohorts. Figure 4 shows the cumulative number of live births born to women of different birth cohorts by different ages. It shows that by the age of 45 years, when most women will have completed their childbearing, those born in 1934 had an average of 2.63 live births. Women born in 1955 had an average of 1.95 births by the same age. The graph suggests that completed family size has been falling consistently in recent birth cohorts. This decline could reverse, if recent cohorts of women have more births at older ages, but the figure gives no evidence of any change in the overall trend towards lower fertility.

Figure 4 Cumulative fertility by birth cohort

Source: GROS

Fertility rates in Europe

Fertility rates throughout Europe have been declining for the past 20-30 years. Other north and west European nations have seen similar trends to those in Scotland, with rising mean age of motherhood and fertility rates falling from the 1960s. In southern European countries like Spain and Italy, the decline in fertility started later but these countries now have extremely low fertility rates. Table 7 shows total fertility rates in selected European countries.

Table 7 Total fertility rates in selected European countries, 1997

Source Council of Europe

What affects fertility?

To project future trends in fertility rates, we need to understand the factors that may influence them. There is a large literature on the determinants of fertility rates. Contraceptive technology has an obvious impact but the scope to make further changes to overall fertility is probably limited where effective contraception is already widely available. Short term effects may be apparent following problems such as 'pill scares'. Advances in infertility treatment will also have marginal effects on overall fertility rates.

Social trends in marriage and cohabitation have an obvious impact on fertility. Economic trends may also be important. If the average income rises, families can afford to raise more children. However, if women's income rises, the opportunity costs of taking time to raise children also rise. Changes in taxes and benefits may also alter the relative benefits of work and childcare. Such economic influences probably influence the timing of births more than the overall number of children a family may have. A range of cultural factors has been studied and found to correlate to fertility rates and people's fertility aspirations. These include religious values, national pride and perceived norms regarding family size.

Projected fertility rates

It is not possible to predict future fertility with certainty. Population projections from the Government Actuary's Department use cohort family size because it is less sensitive to short term influences. The completed family size for Scotland has been lower than the rest of the UK and this is expected to continue. For the latest published projections, the Government Actuary's Department assume the completed family size will continue to decline until around the 1975 birth cohort and eventually level off. These assumptions are based on family building patterns to date and information from the General Household Survey about the number of children women expect to have. However, such information suggests age specific fertility rates will be higher at all ages than the observed rates in 1999. This seems unlikely in the face of recent experience in Scotland. Whereas recent trends have seen increasing rates in older women, rates in younger women have continued to fall.

On request, the Government Actuary's Department performed a "low fertility variant" projection and a "very low fertility variant" projection that assume that age specific fertility rates will converge to eventually give a period total fertility rate of 1.6 and 1.4 respectively, compared to their published estimate of 1.75. The projection using completed family size 1.6 still gives age specific fertility rates higher at all ages than the observed rates in 1999, when the observed total fertility rate was 1.5. The results from both of these projections from the Government Actuary's Department are presented, together with results using the Age Specific Fertility Rates observed in 1999.

Projected births

An estimate of the number of births expected each year is calculated by applying the projected fertility rates to the projected population of women at each age. The projected population of women of each age in each year was obtained from General Register Office for Scotland. Three different sets of age specific fertility rates were applied to these populations: age specific fertility rates projected by the Government Actuary's Department for each year, using the low and very low variants discussed above, and simply using the age specific fertility rates observed in 1999. Table 8 presents the total number of births that would be expected in Scotland using these three different fertility assumptions.

Table 8 Total births expected in Scotland under different fertility assumptions, 2000-2010, in thousands

*Source GAD

In 1999, fertility rates in Greater Glasgow and Lothian were lower than the Scottish average, whereas fertility rates in Highland, Borders and Dumfries and Galloway were higher than the Scottish average. Tables 9-11 present the projected numbers of births to residents of each Health Board area in Scotland, using the three fertility assumptions discussed above and adjusting for these local differences. Table 9 gives estimates obtained by applying the 1999 age specific fertility rates for each health board area to the projected populations for that area. Estimates given in Tables 10 and 11 use the Scottish age specific fertility rates applied to the projected populations of each area, adjusted by applying a scaling factor to take account of local variations in fertility. The figures must be treated with caution because there may be local changes in fertility rates or unexpected migration of women of reproductive age into or out of the area.

Table 9 Total births expected in Scotland by Health Board area, 2000-2010, using observed 1999 age specific fertility rates and projected population of women of reproductive age, in thousands

Table 10 Total births expected in Scotland by Health Board area, 2000-2010, using the Government Actuary's Department low fertility age specific fertility rates projections and projected population of women of reproductive age, in thousands

Table 11 Total births expected in Scotland by Health Board area, 2000-2010, using the Government Actuary's Department very low fertility age specific fertility rates projections and projected population of women of reproductive age, in thousands

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