Adolescent sexual activity in Britain and the U.S.

Improvements in contraceptive use among adolescent females have contributed significantly to a decline in pregnancy rates in Britain and the United States, according to a multidecade comparison of the two regions. The joint British and American study in the Journal of Adolescent Health, however, found a steeper decease in pregnancy rates in the United States, likely due to a recent decline in sex in that country, but not in Britain.

The authors noted that despite the reduction in pregnancy rates among adolescents, aged 16 to 19, in Britain and the United States, they remain high compared to other high-income geographic areas. 

Methods
The study used data from two rounds of the U.S. National Survey of Family Growth (conducted between 2002 and 2003 and between 2011 and 2015) and the British National Survey of Sexual Attitudes and Lifestyles (conducted between 2000 and 2001 and between 2010 and 2012). Pregnancy rates were calculated from data on national births and abortions.

Findings
Although pregnancy rates declined in both countries, the declines in rates began earlier and were more pronounced in the United States, decreasing 45% from 2001 to 2013, 11% from 2001 to 2007 and 38% from 2007 to 2013. But rates were fairly stable in England and Wales from 2001 to 2007, followed by a reduction of 34% from 2007 to 2013. 

The study also concluded that in 2001, the pregnancy rate among adolescent women was substantially higher in the United States than in England and Wales: 94 and 70 pregnancies per 1,000 adolescent women, respectively. By 2013, though, this gap narrowed: 52 and 46 pregnancies per 1,000 adolescent women, respectively.

In addition, a higher proportion of adolescents in Britain in 2010 than in the United States in 2013 reported ever having had sex (65% vs. 49%), along with sex within the last year (64% vs. 45%), sex within the last 6 months (59% vs. 45%) and sex within the last 4 weeks (48% vs. 45%). 

For the same time periods, the differences between the two regions were greater for more recent sex. For example, in Britain in 2010, 74% of those who reported ever having had sex also reported sex within the last 4 weeks, compared to only 59% in the U.S. in 2013 (P < .001). 

Likewise, in the later study periods, 50% of adolescent women in Britain who had ever had sex reported having sex four times or more within the last 4 weeks as opposed to 32% of adolescent women in the U.S. who had ever had sex (P < 0.001).

In both regions, there was also a trend toward more effective contraception. However, a higher proportion of adolescent women in Britain reported using more effective contraception: 68% vs. 52%, respectively (P < 0.001).

Between 2000 and 2010, there was no change in the proportion of British adolescent women reporting nonuse of contraception. But in the United States, the proportion typically using no method declined from 8% to 4% between 2002 and 2013 (P = 0.02). 

Furthermore, although neither region saw an increase in the proportion of adolescent women usually employing more effective methods of contraception overall, use of an intrauterine device (IUD) or implant increased in both locations: from 1% to 13% in Britain (P < 0.001) and from 1% to 5% in the United States (P = 0.02). In the later study period, a higher proportion of adolescent women in the U.S. also normally used condoms than those in Britain: 36% vs. 27% (P = 0.020). However, a markedly higher proportion of US adolescents typically used withdrawal: 8% compared with less than 1% in Britain (P < 0.001).

Overall, the proportional decline in the pregnancy risk index (PRI) was substantially larger in the United States: -33% vs. -20% in Britain.