Girls who became pregnant before age 15 were more likely to report having sex with much older partners and initially forgoing contraception than their slightly older peers, according to a new study.
Nearly 36 per cent of girls who first got pregnant before age 15 had sex for the first time with a partner at least six years older, compared to 17 per cent of girls who got pregnant between 15 and 19.
That statistic "is very serious and represents complicated relationships with unequal power," said lead author and obstetrician Dr. Marcela Smid, from the University of North Carolina at Chapel Hill. She worked on the study while at the University of Chicago.
To make better use of public health awareness and intervention campaigns, Smid and her team wanted to know more about how very young teens were at risk of becoming pregnant.
They used data from the National Survey of Family Growth collected between 2006 and 2010. A total of 3,384 women reported on the survey that they had their first pregnancy before age 20. Within that group, 289 women had become pregnant before age 15 and the rest between 15 and 19.
Girls who became pregnant before age 15 were twice as likely as older girls to be Hispanic or black, the researchers found.
Younger pregnant teens were less likely to have been living with both biological parents at age 14 and less likely to have been brought up within the Catholic or Protestant religions.
Only 25 per cent of the youngest teen group reported using contraceptives the first time they had sex, compared to 56 per cent of older girls.
While it is "a little bit easier to study live births with national survey and surveillance data," those statistics don't tell the complex story of pregnancies, Smid said.
Many pregnancies among very young girls end in miscarriage or abortion, she noted.
"We know that their risk of poor pregnancy outcomes is the highest of any age group, even when compared with women who get pregnant at age 45," Smid said.
In general, US teen pregnancy rates have gradually declined, but, for the youngest teens especially, "any pregnancy rate above zero is too high," she said.
About one in 1,000 girls under the age of 15 became pregnant in 2008, the researchers write in the journal Obstetrics and Gynecology. That compares with about 68 per 1,000 girls between ages 15 and 19.
The researchers also found that 89 per cent of the under-15 group did not want to become pregnant in the first place, compared with 75 per cent of teens between ages 15 and 19.
"There are still things we don't know," Smid said. "For example, we looked at the first sex experience, but we don't know the circumstance or the partner involved in the first pregnancy."
"Measuring pregnancy intention is an extremely complicated thing to do," said Phillip Levine, an economist at Wellesley College in Massachusetts who has studied teen pregnancy.
"Asking someone years after the fact what was going on in their minds during the act - that's difficult to untangle," he said.
Women in the new study were in their early 30s, on average, when asked about past pregnancies.
Levine also noted that for some girls, tough economic and family situations mean there's not much of an incentive to avoid early pregnancies.
"What we need to consider to fix the problem is think about how these disadvantages contribute to teens becoming pregnant," Levine, was not involved in the current study, told Reuters Health.
"Teens must want to avoid getting pregnant, or else it doesn't matter what the intervention is," whether sex education or better contraceptive access.
If young girls are already on a path that does not include college or a job that leads to a change in socioeconomic status, then having a baby may not seem like such a bad idea, he explained.
"A lot of the problem is about opportunity," Levine said.
"We live in a society where income inequality is large and growing," he said. "Teen pregnancy can be seen as a symptom of this broader problem. We need to find ways to allow people to be upwardly mobile."