At a time when the medical community has been heartened by a decline in risky sexual behavior by teenagers, a different problem has crept up: More adult women are forgoing birth control, a trend that has experts puzzled -- and alarmed about a potential rise in unintended pregnancies.
Buried in the government's latest in-depth analysis of contraceptive use was the finding that the number of women who had sex in the previous three months but did not use birth control rose from 5.2 percent in 1995 to 7.4 percent in 2002. That means that as many as 11 percent of all women are at risk of unintended pregnancy at some point during their childbearing years (ages 15 to 44).
Researchers at the National Center for Health Statistics took pains to point out that the "increase is statistically significant" and that the "apparent change merits further study." Other analysts called the spike a troubling development that translates into at least 4.6 million sexually active women at risk of conceiving a child they had not planned on.
Because the survey is so large (more than 7,600 women) and known for its accuracy, "an increase of even two percentage points is worrisome," said John S. Santelli, a professor of population and family health at the Mailman School of Public Health at Columbia University. Even as he cheered the news that a growing number of teenagers are using contraception, Santelli wondered whether doctors are neglecting women.
"Maybe we're failing with women over 21," Santelli said.
Although unintended pregnancies can be welcome surprises, the danger from a public health and societal standpoint is that many of the women are financially or psychologically unprepared for parenthood at that point in their lives.
The number of unintended pregnancies "is a very difficult concept to measure accurately," said James Trussell, director of the Office of Population Research at Princeton University and an authority on contraceptive trends.
In analyzing previous reports by the National Center for Health Statistics, Trussell has determined that half of all unintended pregnancies occur among the more than 95 percent of women who used some type of contraception, probably because the method failed or was used improperly. That means the other half of unintended pregnancies came from the sliver of the population not using birth control.
"That is why this is of enormous concern," he said in an interview. "This tiny minority contributes half of all unintended pregnancies."
The data come from one-on-one interviews with 12,500 women and men ages 15 to 44. Government interviewers, who spent an average of 85 minutes with each person, found that 98 percent of women reported using contraception during their reproductive years, and the pill was the most popular choice, followed by female sterilization -- usually by having their fallopian tubes tied. Female respondents were also asked about their partners' use of birth control methods, such as condoms.