The plunge in teenage birth rates to historic lows has been well-documented, and the Centers for Disease Control and Prevention weighed in Tuesday with its own report on progress over the past 20 years. During that period, births to girls aged 15-19 dropped from 84.1 per 1,000 teens in 1991 t0 29.4 in 2012.

That's very good news, and it shouldn't be minimized.

But the CDC report issued Tuesday also contains some facts that should chill any parent buoyed by the overall results. The CDC's message Tuesday was that more than one-fourth of those children -- some 86,423, or 1,700 a week -- were born to girls aged 15 to 17 in 2012.  That represents a healthy decline of 63 percent in the past 21 years as well. But giving birth that young is associated with a variety of medical risks and emotional, social, and financial costs, including the likelihood that the mother will not finish high school or earn a GED.

From there the information gets more troubling. I'll pick out a few nuggets for you:

• Hispanics (25.5 births per 1,000 girls ), blacks (21.9), American Indians/Alaska Natives (17.0) are much more likely (emphasis mine) to give birth between the ages of 15 and 17 than whites (8.4) and Asians/Pacific Islanders (4.1).

• There's a huge disparity in the birth rate among these youngsters across the country, from a high of 29 per 1,000 in Washington, D.C. to a low of 6.2 in New Hampshire. The report offers no reasons why, and in a telephone news conference, CDC officials said they didn't have enough information to draw conclusions.

Kathryn Kost, a demographer for the Guttmacher Institute, which works on sexual and reproductive health issues, said that figure probably reflects a wide variety of factors including race, poverty, sex education, availability of contraception and abortion, attitudes toward giving birth at a young age and more.

• Kids are using the least effective contraceptives. Only 1 percent used an IUD or hormonal implant the last time they had sex; 22.7 percent used nothing at all. Sixty-two percent used less effective methods such as condoms, cervical caps, sponges, the rhythm method, withdrawal and responses marked “other.”

• Among sexually active teens in this age group, 83.3 percent did not receive formal sex education before the first time they had sex. That contrasts with the 90.9 percent of all 15- to 17-year-olds who received formal education on birth control or how to say no to sex.

"We are missing opportunities to deliver prevention messages before younger teens begin having sex" -- both how to say 'no' to sex and the proper use of contraception, said Ileana Arias, the CDC's principal deputy director.