Teen births across the United States have been declining steadily for the past two decades, and a new study shows that they have reached historic lows.

By collating data from birth certificates nationwide, the U.S. Centers for Disease Control and Prevention (CDC) has determined that in 2011 there were only 31.1 births per 1,000 teens between the ages of 15 and 19. This represents a 25 percent drop from 2007, when the number was as high as 41.5.

Historically, there are a few interesting trends in teen birth rates in the U.S. (all data is from the CDC):

The 1957 Peak and the Pill

First, there is the startling jump that began in the 1940s and peaked in the 1950s. Heather Boonstra, in the Guttmacher Report on Public Policy, argued that a drop in marrying age that occurred in the 1950s, combined with the large number of young men returning from World War II, partially explains the trend: There were simply lots of teens looking to start families.

But it was also the last decade before birth control really entered public discourse. According to a PBS report, "anti-birth control laws on the books in 30 states still prohibit[ed] or restrict[ed] the sale and advertisement of contraceptive devices." Then, in the mid-1950s, women's rights activist Margaret Sanger worked with Dr. Gregory Pincus to create the first oral birth control pill. In 1957, the pill, Enovid, was approved by the Food and Drug Administration (FDA) for treatment of severe menstrual disorders; almost immediately, women began to take it off-brand to stop menstruation as a method of contraception. And in 1960, the FDA approved Enovid as a birth control pill. By the 1970s, over 10 million women were on the pill.

The data is striking: teen birth rates peaked in 1957. That same year, the Pill hit the markets, and since 1957, teen births have steadily declined -- with only two exceptions: a brief spike in the early 1990s, and a flat-lining in the early 2000s.

The 1990s Spike

It's unclear exactly why teen birth rates briefly spiked in the late 80s and early 90s. A 1990 CDC Report suggested that "trends in sexual experience among teenagers and variations in the accessibility and use of family-planning and abortion services" were to blame.

But according to the Guttmacher Institute, teen reliance on condoms rose while the use of the pill declined dramatically. And even condom use wasn't as widespread as it should have been. Based on surveys done at the time, American teens were significantly less likely than their European counterparts to use medical means of contraception (such as the pill), and also less likely to use condoms during their first sexual encounters.

In the late 90s, changes in habits and attitudes led to a return to stable decline in teen birth rates -- until the years between 2003 and 2007, when the numbers flatlined: in 2003, it was 41.6 and in 2007, 41.5. Then, in 2007, the numbers started to drop again.

So what happened in the first half of the 2000s?

The Politics of Pregnancy in the 21st Century

Some experts, including Heather Boonstra of the Guttmacher Institute, place the blame squarely on the abstinence-only education programs initiated by the Clinton Administration and then championed by the Bush Administration. According to the Sexuality Information and Education Council of the United States, over $1.5 billion was spent on "unproven" abstinence-only sex ed programs in the 90s and 2000s. The plateau of teen birth rates "coincides with an increase in rigid abstinence-only-until-marriage programs, which received major funding boosts under the Bush administration. A strong body of research shows that these programs do not work," Boonstra said in 2010.

Public officials have been hesitant to concede this fact. Speaking to Time magazine, Bill Albert, the chief program officer of The National Campaign to Prevent Teen and Unplanned Pregnancy, argued that "the short answer [to why birth rates have fallen] is that it is a combination of less sex and more contraception. Teenagers have a greater number of methods of contraceptives to choose from." Although he did not give credit outright to
contraceptive education per se, Albert did add that "programs that have been shown to actually move the needle, that number has grown over the last years, and to the credit of the federal government, they have invested in it."

Public health officials from both Arizona and Utah -- the two states that saw the most significant drops in teen birth rates between 2007 and 2011 -- focused on the efficacy of holistic education programs that attempted to reduce risky sexual behavior while also addressing other issues like self-esteem and community violence. However, both states also confirmed that much of this education is, by necessity, still extracurricular.

In Arizona -- a politically conservative state -- schools are not required to offer sex education at all, but when they do, "abstinence must be stressed."

And Utah, with its primarily Mormon population, takes a very traditional view on sexuality and family planning, with even stronger abstinence-only leanings than Arizona -- Arizona asks that its schools stress abstinence; Utah is an abstinence-only education state. "We've had some trouble in Utah, because we can't do it through schools," said Laurie Baksh, Maternal and Infant Health Program Manager at Utah's Department of Health, acknowledging the difficulty of educating teens in this environment.

So how are Arizona and Utah getting around the issue? In both states, efforts around lowering teen birth rates have left the school and focused on
community teaching opportunities. In Arizona, community-based programs, where "the folks running the programs know their communities," have proven to be a hugely effective way of focusing resources in high-impact communities. It's hard to say what's being taught in these community programs. Sjolander stated that it is a "youth development approach, a movement to help build self esteem, to help young people envision their future, set goals, and feel connected to their communities" -- although what that means will, by its nature, vary from program to program.

In Utah, the downward trends are likely a result of "clinicians in the community starting to educate women about the most effective contraception -- IUDs and implants -- we think some of that education is getting out there," according to Baksh. Utah's success also hinges on community education. Baksh noted the success of the Personal Responsibility Education Program (PREP), a federally funded program that the state government used to create "comprehensive sexual education" programs at the local, community level.

PREP is a cornerstone of the Obama administration's overhaul of nation-wide sex education funding. After three decades of administrations insisting that federal dollars could go solely to abstinence-only programs, in the fiscal years 2010 and 2011, the Obama administration eliminated funding for two-thirds of previously existing abstinence-based programs, and also earmarked new funds for two new sex education programs focused on a more comprehensive, evidence-based approach (PREP is one of these). Early results are showing tremendous success; after teen birth rates flat-lined in the early-to-mid 2000s, they are now dropping.

When it comes to sexual health, it's all about education -- a 2012 study showed that women who did better on a contraceptive test were significantly more likely to use birth control -- and sadly, that's all about money. Both Utah and Arizona emphasized that they couldn't have done what they did
without specially earmarked funding -- federally funded revenue streams that began to flow in 2008 for Utah, and allocated state lottery dollars in Arizona since 2004. Meanwhile, other parts of the country were less lucky, fiscally.

"Our challenge at the state level is that we have no dedicated funding," said Kim Mertz, Director of the Division of Family Health in North Dakota, one
state that saw no change in teen birth rates from 2007 to 2011. "We are really at a point right now where it's a wait and see with our federal grants."