Introduction

This chapter presents trends in a variety of reproductive measures. It looks mainly at the second half of the 20th century and the first few years of the 21st century. Where possible, age differences in the trends are examined.

Much of the data refer to births. For this chapter, the main data source is birth registration data as given by the parents or informant to the local registration service. It has been a legal requirement to register births since 1837 but these data are only computerised and available for analysis from 1963 onwards. Most of the data refer to England and Wales because data for Scotland and Northern Ireland are handled separately in their respective countries but, where possible, data are given for Great Britain or the UK.

Number of births and total fertility rate

The total fertility rate (TFR) is the average number of children a woman would have if she experienced the age-specific fertility rates for a particular year throughout her childbearing life. It is a useful measure of the current level of fertility as it can be used to examine both changes in fertility over time and between populations by removing the effect of different age distributions. However, changes in the timing of childbearing between generations can distort the TFR so, for example, if women are delaying their childbearing to older ages, as in England and Wales during the 1980s and 1990s, the TFR is likely to underestimate eventual average family size.