London School of Hygiene & Tropical Medicine

One in six pregnancies among women in Britain are unplanned, and one in 60 women (1.5%) experience an unplanned pregnancy in a year, according to new results from the third National Survey of Sexual Attitudes and Lifestyles (Natsal), published in The Lancet.

The findings come from the first study to provide population prevalence estimates of unplanned pregnancy in Britain since 1989, and the first ever using a validated multi-component measure (the London Measure of Unplanned Pregnancy).

Researchers led by Professor Kaye Wellings at the London School of Hygiene & Tropical Medicine, in partnership with UCL and NatCen Social Research analysed data from 5,686 women of child-bearing age between 2010 and 2012, drawn from the third National Survey of Sexual Attitudes and Lifestyles (Natsal) survey data.

One in six (16.2%) pregnancies experienced in the past year score as unplanned, 29% as ambivalent (29%), and just over half (55%) as planned. Whilst pregnancies resulting in births were far more likely to be planned than those ending in abortion, the finding that four in 10 pregnancies ending in abortion were planned or ambivalent cautions against equating abortion and unplanned pregnancy.

Study lead author Prof Wellings, from the London School of Hygiene & Tropical Medicine: “Our estimate of the rate of unplanned pregnancies in Britain is lower than estimates in some other high income countries. This may be explained by differences in measurement, but it may also in part be due to contraception being available free of charge from the NHS.”

Pregnancies in young, single women are most likely to be unplanned. Pregnancies in the age group 16-19 account for only 7.5% of the total number of pregnancies for all ages, but 21.2% of those that are unplanned. The majority of unplanned pregnancies, though, occur in women aged 20-34 years, because more pregnancies occur in this age group.

The researchers found factors associated with unplanned pregnancies were having first sex before the age of 16, lower educational level, and not living with a partner. Receiving sex education mainly from school lessons was associated with a lower likelihood of unplanned pregnancy. Recent experiences of smoking, having used drugs other than cannabis, and depression were also more common amongst women reporting unplanned pregnancies, emphasising the need to help women and their partners to modify aspects of lifestyle that could harm their own health and wellbeing, and that of their child.

The paper shows marked generational changes in events related to sexual and reproductive health over the six decades represented by the sample. Average (median) age at first sexual intercourse decreased by two years for men and three years for women, (from 19 for women and 18 for men aged 65-74, to 16 years for both aged under 25 years), whilst age at first cohabitation and first parenthood increased, particularly among women.

Prof Wellings added: “Over the past 60 years, the time between the age at which we first have sex, when we move in with a partner and when we first have children has widened. Women may now spend about 30 years of their lives needing to avoid an unplanned pregnancy.”

• Kaye Wellings, Kyle G Jones, Catherine H Mercer, Clare Tanton, Soazig Clifton, Jessica Datta, Andrew J Copas, Bob Erens, Lorna J Gibson, Wendy Macdowall, Pam Sonnenberg, Andrew Phelps, Anne M Johnson. The prevalence of unplanned pregnancy and associated factors in Britain: findings from the third National Survey of Sexual Attitudes and Lifestyles (Natsal-3). The Lancet. DOI: 10.1016/S0140-6736(13)62071-1