(CNN) In the United States, teen-aged moms are increasingly rare. In 2016, the teen birth rate dropped 9% compared to the previous year, a new government report published Friday found. This record low for teens having babies continues a long-term trend.

The birth rate among teen girls has dropped 67% since 1991, according to the National Center for Health Statistics, which presented preliminary data for 2016 based on a majority (99.9%) of births.

In 2016, the number of US births totaled 3,941,109, a decline of 1% compared to 2015. The fertility rate of 62 births per 1,000 women is a record low for the nation.

The teen rate is a "phenomenal decline," said Dr. Elise Berlan, a physician in the section of adolescent medicine at Nationwide Children's Hospital. Berlan, who did not conduct this research, said the reason she's so excited is "because we know that the vast majority of teen births are unintended."

What's fueling the declines?

"Data [from previous years] really suggests it is access to contraceptives and use of contraceptives that has really led to these kind of changes," said Berlan, who noted that "most teens are using some form of birth control" and the top method is "the condom, followed by withdrawal and the pill."

Older moms

On the flip side, the increase in births to older moms is also important, said Martin.

For women between the ages of 30 and 34, the birth rate increased by 1% over 2015 -- the highest rate for this age group since 1964. The birth rate for women who are between 35 and 39 is up 2% over 2015, representing the highest rate since 1962.

Even older women, those between the ages of 40 and 44, showed a swelling increase of 4% over 2015 -- the highest rate for this group since 1966, according to the statisticians, while the rate of birth for women who are older than 45 is also a record high though the number of births remains essentially unchanged compared to last year.

Joyce A. Martin, a co-author of the report and lead statistician, also noted the declining rate of nonmarital births -- births to people who aren't legally married -- in 2016, which fell 3% compared to the previous year.

The report, first in a new annual series, provided additional vital statistics.

Prenatal care

Three out of four woman got prenatal care in their first trimester, noted Michelle J.K. Osterman, a co-author of the report and statistician. That said, 6.2% of pregnant women in 2016 had late prenatal care (beginning in the third trimester) or no prenatal care.

"In a perfect world, every woman would get early prenatal care," said Osterman. She noted that "2016 is the first year for which we have national data" measuring prenatal care, so there can be no comparisons to previous years.

The percentage of women receiving prenatal care beginning in the first trimester of pregnancy ranged from 51.9% for non-Hispanic native Hawaiian and other Pacific Islanders women to 82.3% for non-Hispanic white women. Nearly 81% of Asian women also received prenatal care, while 72% of Hispanic and 67% of non-Hispanic black women did the same.

"We want to bring everybody up to an overall rate of over 80%," said Martin.

Sarah Verbiest, executive director of the Center for Maternal & Infant Health in the University of North Carolina School of Medicine, noted the "inequities among who is getting early access to care" during pregnancy. Verbiest was not involved in the research.

"We know that the growth of the baby happens really fast, really soon. So in the first nine weeks, all of the key parts of the baby are formed," said Verbiest. Prenatal care in the first trimester helps a pregnant woman learn what changes to expect and address any unhealthy factors in her life.

"If someone has diabetes and it's not really well-controlled that could lead to birth defects," said Verbiest. "Right away, you want to be helping her manage diabetes or any chronic conditions."

Pregnant women also need to be taking vitamins while eating and exercising in healthy ways. Prenatal care helps reduce all potential risks as early as possible and leads to healthier babies, explained Verbiest.

Shift in preterm births

"For many years in this field we saw that women who are Hispanic had really good birth outcomes -- even in the face of some more challenges in terms of accessing care," said Verbiest. "We always said, 'Thank heavens for that.'"

However, the new data suggests there may be a shift.

For example, the overall rate of low birthweight rose for the second straight year to 8.2% in 2016 from 8.1% in 2015. The rate among Hispanic woman was 7.3% compared to about 6.9% for white women.

Verbiest worries that Hispanic women may be adopting some of the "not healthy habits in this country," including unhealthy eating and lifestyle, while also being affected by "community stress that isn't good for pregnant women."

This is the second year in a row for an undesirable rate of low birth weights, noted Verbiest.

"It's not the direction we want it to go," said Verbiest. "We know that the outcomes for babies who are too thin and too small are not as good -- they start life out like a step behind" children who are born at a normal weight at full-term, about nine months.

The preterm birth rate -- when a baby is born more than three weeks before a full nine month pregnancy -- also rose for American women overall. Preterm births can lead to poor health for babies.

Martin said the increase in the preterm birth rate was not a "small one -- a 2% rise is fairly substantial. At a minimum, it tells us the improvements that have been going on for the last decade [appear] to have stalled."

On the positive side, Verbiest celebrated the declining rate of cesarean births noted in the report.

The rate of C-sections decreased for the fourth year in a row to about 32%, having peaked in 2009 at about 33%.

"That is the result of work across all kinds of partners in this country," said Verbiest. Patient advocate groups, payers such as insurance companies and Medicaid, nurses, physicians, and midwives all have worked hard to bring that trend line down, she said.

Access to care

Both Verbiest and Berlan see access to health care as crucial to achieving the best results for women's health, particularly pregnancy and birth.

"Putting restrictions on teens' access to birth control could really have some profound effects on unintended births in those folks," said Berlan. The hospital where she works requires parental consent for teen patients since her home state of Ohio lacks a statute protecting a minor's right to access contraception confidentially.

"We certainly see teen girls and young women coming to the office with their parents. And that's really just a wonderful thing to work with a mom-daughter [pair] on these important decisions," said Berlan.

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"The other side of it, though, is a lot of teens need confidential access to birth control and it's important to preserve that," said Berlan.

The "significant differences in how babies are getting a start in life" speaks to "larger issues," such as health care access, that need to be dealt with by our society, said Verbiest. "All of our sweet babies and families should get to have the best start."