Teen birth rates have dropped again, reaching a historic low, and fewer babies are being born early or with a low birth weight, a new U.S. government report shows.

The improvement may be led by many factors."We talk more about teen pregnancy, the responsibility of having a child and how difficult it is to be a teen mom. We also talk about contraception and abstinence more," said Dr. Jill Rabin, chief of ambulatory care, obstetrics and gynecology at Long Island Jewish Medical Center.

The report, from the National Center for Health Statistics branch of the U.S. Centers for Disease Control and Prevention, documented declines in the three areas: The teen birth rate fell to 31.3 births per 1,000 women aged 15 to 19 in 2011. Twenty years ago, that rate was 61.8 per 1,000 teenage girls. And, for the fifth straight year, the preterm birth rate dropped, to 11.7 percent in 2011 from 12.8 percent in 2006. The rate for low-birth-weight babies also declined, from 8.15 percent in 2010 to 8.1 percent in 2011.

Teen pregnancy rates have been declining for years. In April, a Centers for Disease Control and Prevention report showed an all-time low for teen birth rates in 2010 at 34.4 births per every 1,000 women between 15 and 19 years old. That reflected a 44 percent drop in teen birth rates from 1991 to 2010, and there were fewer teenage mothers in 2010 than any year since 1946.