Younger women, blacks and women with a high number of recent life disruptions are more likely than their counterparts to get second-trimester abortions, a new study finds.

The research focuses on a relatively small group of American women, those who end pregnancies after the first trimester, which lasts 12 weeks. As of 2006, 88 percent of abortions occurred before the end of the first trimester, making second-trimester abortions relatively rare. These later abortions, however, are more expensive, more difficult to come by, and carry more medical risk than earlier procedures, according to the Guttmacher Institute, a reproductive health research organization.

There is no medical definition for when an abortion becomes "late term," though many sources place the line at after the 20th week of gestation. According to Planned Parenthood, medical risks from abortion such as an incomplete abortion, infection, or injury to the cervix or other organs increase the longer a pregnancy continues. Until 20 weeks gestation, the risk of death to the mother from childbirth is 11 times greater than the risk of death from an abortion. But after 20 weeks, the risk from abortion and childbirth are about the same.

The Centers for Disease Control and Prevention (CDC) keeps some data on second-trimester abortions, but the only demographic information available from those records is age and race. According to the CDC, teens, black women and Hispanic women are more likely than older adults or other races to get second-trimester abortions — but that data is limited. For example, it doesn't include California, site of 18 percent of all abortions in the U.S.

Second-trimester abortions

To get more comprehensive information, Guttmacher Institute researchers surveyed 9,493 abortion patients at 95 hospitals and clinics across the country in 2008, weighting the data to create a nationally representative sample of abortion patients. They queried the women on demographic factors like race, poverty, education and marital status, as well as asking them about domestic violence, health insurance, and recent disruptive life events, including unemployment, serious medical problems and death or illness among friends and family.

They then focused on women who had abortions after 13 weeks. Within that group, they compared women who had 13-to-15-week abortions with those who had abortions after 16 weeks.

"We kept seeing all these discussions of second-trimester abortions and attempts to limit abortions by trimester," Guttmacher senior research associate Rachel Jones told LiveScience. "It dawned on us that we didn't know anything about this population."

Of all women surveyed, 10.3 percent had abortions after the first trimester. These women were more likely to be young, black, less educated and living in poverty than women who had earlier abortions. They were also more likely to have experienced violence at the hands of the man who got them pregnant and to have dealt with at least three serious life events in the last year.

Compared with the 10.3 percent overall number, 14 percent of patients under age 18 had second-trimester abortions, as did 13.8 percent of adolescents ages 18 to 19. Among all ages, 13.4 percent of black abortion patients had second-trimester procedures, compared with 8.5 percent of white abortion patients and 9.9 percent of Hispanic abortion patients. [5 Myths About Women's Bodies]

Of abortion patients without high-school diplomas, 13.1 percent had second-trimester abortions, a proportion that decreased with education. Of college-graduate abortion patients, only 5.8 percent had late abortions. A lack of education may mean that patients are less health-literate, and thus less likely to figure out how to access an abortion until later in pregnancy, the researchers wrote in their report released today (Dec. 16) and to be published in an upcoming issue of the journal Contraception.

Living under the poverty line also increased the chances of a later-term abortion, with 12.6 percent of abortion patients living in poverty getting second-trimester procedures. The rate of second-trimester abortions dropped to 7.7 percent among women earning at least twice as much as poverty levels.

Abortion access

Physical abuse or rape by a partner increased the likelihood of later abortion, with 13.7 percent of abortion patients who'd experienced second-trimester procedures (compared with 10 percent of women who hadn't). Other disruptive life events — loss of a job or a partner, for example — were likewise linked to later abortions. Of abortion patients who'd experienced three disruptive events in the last year, 14.8 percent got later-term abortions.

Experiencing disruptive events may prevent women from noticing their pregnancy early enough to get a first-trimester abortion, the researchers wrote in their report. Life chaos may also prevent women from accessing an abortion early. Alternatively, some women may have planned to continue their pregnancies until their circumstances changed, forcing them to seek an abortion later rather than earlier.

Using health insurance to pay for an abortion was also linked with later procedures. Slightly more than 13 percent of women on private insurance or Medicaid got second-trimester procedures compared with 8.2 percent of women paying out-of-pocket.

The overrepresentation of health insurance payers among women getting second-trimester abortions could be because the procedure is expensive, Jones said, and thus only women with insurance can afford it. Additionally, she said, most women who get first-trimester abortions pay out of pocket because they don't want the abortion to appear on their health insurance records. For the more expensive second-trimester procedure, women might give up that confidentiality in order to secure the money for the surgery.

For women who got abortions after 16 weeks of pregnancy, later in the second term, age and education were not factors. Black women, however, were still more likely than other races to get abortions this late. Wealthier women and women paying with insurance were also more likely to get abortions after 16 weeks, likely again because of the prohibitive cost of the procedures.

The majority of patients who had second-trimester abortions indicated they would have preferred to have them earlier, the researchers reported. While later abortions are unlikely to be eliminated — for example in cases where women find out about fetal anomalies late in the pregnancy — they could be reduced, Jone said.

"Prior research has found that things like finding an abortion provider, making arrangements and tracking down the money are barriers," she said. "If we remove these barriers to first-trimester abortion services, this could potentially decrease the need for second-trimester abortion services."

The full report is available as a PDF online.

You can follow LiveScience senior writer Stephanie Pappas on Twitter @sipappas. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.