When those accidents happen, older women are more likely to abort than any other group. And, as the abortion rate for other ages has declined in recent years, the rate among women in their 40s has risen slightly.
Doctors and nurses who treat women in perimenopause -- the transition to menopause -- say the moral is clear: Just because a woman's age makes her unlikely to get pregnant does not mean she's safe.
Dr. Francis Boudreau, chairman of obstetrics and gynecology at Caritas St. Elizabeth's Medical Center, said he's seen women who decide in their mid-30s that they're done having children; then, a few years later, "They sort of say, `I'm 40 and I don't have to be careful.' "
"They think they're calling it quits and the next thing you know, they're getting a surprise," he said. "It's not easy to get pregnant, but you still can get pregnant, and if you're not careful, you will get pregnant."
Overall, the rate of pregnancy, both accidental and intended, among older women is quite low: In 2000, there were only 11 pregnancies among every 1,000 women in their early 40s, compared to 159 for women in their early 20s.
But for women over 40, just over half of pregnancies are unintended -- a rate second only to teenagers, according to 1994 data, the most recent available from the Alan Guttmacher Institute, a nonprofit group that tracks abortion, among other reproductive trends.
And, in 2000, 31 percent of pregnancies to women over 40 ended in abortion -- again, second only to teenagers, also according to Guttmacher surveys.
Older women are likelier to conceive babies with genetic flaws that could prompt them to abort, but the figures do not reveal how great a factor that is in the abortion rate.
What the numbers do seem to show, however, is simply a greater determination among older woman not to bear an unwanted child. Among women over 40 facing unintended pregnancies, nearly 65 percent of those pregnancies ended in abortion, the highest percentage of any age group, according to the 1994 Guttmacher survey.
No more detailed research has been done into the reasons for such high abortion rates, said Rachel K. Jones, a senior research associate at the Guttmacher Institute. But she said the rate could be related to a more general trend -- that, overall, two-thirds of the women who get abortions already have children.
Older women are especially likely to have children already, she said, "and they know what having a child entails -- the time, energy and expense." Also, the more children a woman already has, the less able she may be to take on another baby, Jones noted.
Older women are less likely to get pregnant because the quality of their eggs tends to decline with age, among other reasons. But the overall pregnancy rate for older women is also low in part because many women or their partners have been surgically sterilized by then, said Stanley Henshaw, a senior fellow at the Guttmacher Institute.
Among women over 40 using a method of birth control in the 1994 survey, he said, 50 percent reported it was their own sterilization, 20 percent said their male partner had been sterilized, and 12 percent were taking pills.
For those who have not been sterilized, Jennie Mastroianni, a nurse-practitioner with 20 years of experience in women's health, has some advice: Don't assume menopause has kicked in until a full year after periods stop.
During perimenopause, women tend to grow lax about birth control because they think there's little risk and hear so many horror stories of older women unable to conceive, said Mastroianni, who works at Bay State Reproductive Medicine in Westborough. But "every woman is unique and their ability to get pregnant is different."
Because a woman's menstrual cycle becomes less regular during perimenopause, it is harder to use the rhythm method, Mastroianni said. A woman who is used to a 28-day menstrual cycle, and who has prevented pregnancy by avoiding sex between days 8 and 16, could suddenly find her cycles lasting 40 or 21 days, and previously "safe" days might no longer be. Or, a woman could have a three-month break in periods before they return, she said.
For all the warnings, however, many "surprise" children born to older women do end up very much wanted and loved, Boudreau said.
One of his patients, Maureen Quinlan of Walpole, gave birth two months ago to identical twin girls -- Caroline Rose and Catherine Jane -- at the age of 41. She and her husband, Kevin, who already had three children together, had not been trying to conceive, but also had done nothing to prevent it, Quinlan said.
They were happy when they found out she was pregnant, she said, though, when the ultrasound technician spotted the second fetus for the first time, Kevin inquired jokingly whether there was a cardiac specialist nearby.
"I just think children are such an incredible sign of hope," Quinlan said. "And you just let them transform you."
Carey Goldberg can be reached at email@example.com.
© Copyright 2003 Globe Newspaper Company.