New U.S. birth health numbers hint that access to, or the quality of, prenatal care may have gotten worse for some groups of women between 2014 and 2015.

A team at the U.S. Centers for Disease Control and Prevention published the numbers in a new report on U.S. births in 2015.

The team included data on how the percentage of babies born three or more weeks early and the percentage of babies weighing less than 5 pounds 8 ounces have changed from 1989 to 2015.

        • For white mothers, the preterm birth percentage fell to 8.88 percent in 2015, from 8.91 in 2014, and from 8.94 percent in 2013.

        • For black mothers, the preterm birth preterm increased to 13.41 percent in 2015, from 13.23 percent in 2014, and from 13.25 percent in 2013. The preterm birth percentage was the highest since 2012, when it stood at 13.48 percent.

        • For Hispanic mothers, the preterm birth percentage increased to 9.14 percent in 2015, from 9.03 percent in 2014, and from 9.08 percent in 2013. The preterm birth percentage was at the highest level recorded since 2008.

Because the preterm birth rate got worse for black and Hispanic mothers, the preterm birth rate for all births rose to 9.63 percent in 2015, up from 9.57 percent in 2014, and up from 9.62 percent in 2013.

The numbers for low-birthweight births followed a similar pattern.

Related: How has ACA affected people’s health?

The reported percentage of babies born early or with low birthweight can be affected by many different factors including the mother's age. (Photo: iStock)The reported percentage of babies born early or with low birthweight can be affected by many factors, including the mother’s age. (Photo: iStock)

Some of the factors that affect birth weight include the age of the mother, the weight of the mother, the underlying health of the mother, outbreaks of infectious diseases, and changes in how hospitals or government agencies handle birth statistics.

But government researchers believe that providing good health care for women, before and after they become pregnant, can help reduce the incidence of premature birth and low birthweight.

Related: More private plan users report medical bill problems

Information about indicators showing how U.S. health quality changed between 2013, before major Affordable Care Act health coverage expansion programs took effect, and 2014, when the programs took effect, are just starting to come in.

Information about any changes between 2014 and 2015, and between 2015 and 2016, is harder to come by.

One study, by Kosali Simon of the University of Indiana and two colleagues, found that ACA coverage expansion improved the health of low-income, childless adults enough between 2012 and 2014. This research deducted that the group in question gained the ability to work one extra day per month, and found that low-income, childless adults lost just 9.3 workdays due to poor health in 2014, down from 10.4 percent work days per month in 2012.

But CDC reports have shown that some health care access and health outcomes indicators started to level off between 2014 and 2015, and that some got a little worse between 2015 and this year.

The CDC reported in November, for example, that the percentage of “not poor” people under age 65 who reported medical bill problems increased to 12.6 percent during the first half of 2016. That was up from 12 percent in 2015. 

The CDC researchers write in their report that they do not know why the preterm birth and low-birthweight birth rates increased in 2015.

They noted that the preterm birth rate increased by a statistically significant percentage in Arkansas, California, Nebraska and New York state. 

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