A new study from the CDC shows teen births in the US have hit an all-time low, dropping to just over 34 births per 1,000 women who are between 15 and 19 years old — a decrease of nine percent in the last two years alone.

The current numbers are 64 percent lower than the all-time high seen in 1957, and they mark the fewest teen births nationwide since record-keeping began in 1946. And since the United States spends almost $11 billion annually on health costs associated with teen childbearing, the public health impact of the decline is significant.

So why have the numbers dropped so much?

Researchers credit the use of contraceptives, and Dr. Lawrence Friedman, director of adolescent medicine at the University of Miami Miller School of Medicine, said, “There is [also] more awareness of the negative effects of pregnancy and sexually transmitted diseases.”

Possibly proving his point is the fact that Mississippi, which has 55 births per 1,000 young women — the highest in the country — doesn’t require sex education in schools, but when classes are taught, abstinence-only education is the state standard.

New Hampshire, on the other hand, has the lowest teen birth rate in the US with about 16 per 1,000 girls, and requires comprehensive sex-ed in schools. Classes there do include abstinence education, but also information about condoms and contraception.