CHICAGO – Kimberly Dearth’s biological clock was beginning to tick pretty loudly. So when she discovered she was pregnant, she had no problem putting diapers before a diamond ring.

“It was unplanned but not unwelcome,” said Dearth, 37, who is raising her 15-month-old daughter, Samantha, as a single mother. “Two different doctors told me that I would need fertility treatments. So when I found out that I was pregnant, I was shocked, I was frightened, but I was also very happy.”

Dearth, a medical assistant from Cedar Lake, Ind., is among a growing number of women over 35 – when fertility rates begin to steeply decline – to become single mothers.

The number of out-of-wedlock births has reached a record high in the U.S., with nearly 4 in every 10 babies born last year to unmarried women, according to a recent report by the federal Centers for Disease Control and Prevention. The increase was seen in all racial groups.

Unlike two decades ago, teenagers – who are having fewer babies – are not driving the trend. It is fueled, in part, by women in their 30s and 40s, many of whom had put off marriage and family for careers. And single mothers have fought to remove the stigma of raising children out of wedlock.

Married women also are having babies later, researchers said. More than a quarter of the 4.1 million babies born in 2005 were to women ages 30 to 54.

“This is continuing a trend that has been going on for quite a number of years,” said Stephanie Ventura, a statistician with the CDC’s National Center for Health Statistics, speaking of unwed and married older mothers. “We’ve only seen greater rates in the 1950s when people tended to have larger families.”

Fourteen years after actress Candice Bergen drew the ire of Vice President Dan Quayle and other conservatives when her TV character, Murphy Brown, got pregnant and decided to raise the baby alone, single women are helping redefine the typical American family.

Despite efforts by social conservatives to promote traditional marriages, the Ozzie and Harriet stereotypes of the 1950s – a mother who stays home with the children while the father works – have long vanished from most American households. With nearly half of marriages ending in divorce and more couples in non-traditional relationships such as cohabitation, married couples have become a minority, accounting for 49.7 percent of households, according to the U.S. Census.

With marriage no longer considered by many a prerequisite for having children, single mothers are integrating into the mainstream and getting attention in the media, including celebrities like Angelina Jolie and photographer Annie Leibovitz.

Though some pregnancies are unexpected, many older women have gone to great lengths to give birth, such as turning to in-vitro fertilization using sperm banks or donor eggs, health officials said.

“Society’s attitude has changed a little in that people understand that this is an option for single women who have not found the right man, or were divorced in their 30s, and really do want to be a mother,” said Jane Mattes, 62, who founded the networking group Single Mothers by Choice.

According to Mattes, the Internet-driven group has grown from eight members in 1981 to 2,000. Most are college-educated women age 35 to 45 with established careers, debunking the negative stereotype of struggling young mothers on welfare.

“When you hear the term “single mother,’ most people think of teenagers or a divorced woman who was left with children, but most of these women aren’t either,” said Mattes. “They are choosing to become single mothers. … This is about making a personal choice.”

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