Once upon a time, the hit HBO series “Sex and the City” was about four smart women in their early 30s who wanted to have fun and indulge their sexual appetites. These days, as the characters slide toward 40, each is coming to terms in her own way with the consequences of having put off motherhood. Should she have a baby? Now that she has a baby, is she a good mother? She definitely doesn’t want a baby. She’s anxiously trying to have a baby -- can she even have a baby?

These dilemmas are being faced by millions of women who have delayed motherhood in favor of careers and lifestyles far more liberated than those of their mothers. Now, as the biological clock continues to tick, time runs short for making a choice that will forever affect their lives. As women age, that internal dialog grows ever louder and more insistent, says Diana Dell, MD, a reproductive psychiatrist at Duke University Medical Center.

That’s why Dell co-wrote the book, Do I Want to Be a Mom? with Susan Erem (Contemporary Books, $14.95). “Women didn’t used to have much of a choice about whether or not to become mothers, and now they perceive that they do,” says Dell, who is board certified in both obstetrics/gynecology and psychiatry. “And they want to make the right choice.”

That struggle has spawned an entire self-help category for women, visible in Web sites, books, and advocacy groups. In addition to the fact that more women are having babies later in their lives, a growing number of women are choosing not to have children at all. The decision process and its aftermath can be a source of significant distress, says Dell. “As women feel their options narrowing, and contemplate roads not taken, there is often a deep unhappiness, a sense of loss.”

Dell’s book and psychiatric practice are among many services at Duke for women grappling with the motherhood issue, which include clinics, support groups, counseling, and fertility treatments. Brief chapters have provocative, conversational titles that call out to women contemplating motherhood from different points of view: “Age Matters,” “What Does Having Children Do to a Relationship?” and “Will I Be a Good Mom?” Based on hundreds of interviews that Dell and co-author Erem conducted, the book invites readers to peruse the topics that interest them most, in whatever order they prefer.

“I don’t think I really wanted kids a lot until I was 35,” says Sara, a woman quoted in the book. “When I was growing up, the emphasis was much more on getting an education. I was told, ‘Don’t get married until you have a college degree. Get your education so you can take care of yourself no matter what.’”

Women in the book are struggling with their choices, and their voices validate common fears and obstacles. That’s almost as soothing as a support group to an anxious might-be mother, Dell says. “Hearing other women’s stories tends to be very normalizing for people.”

The book speaks to women who may want to have a baby on their own and women in same-sex relationships. Even pregnant women and mothers will see themselves in Dell’s book. Some women have already made the decision to have children or not, but they find themselves wanting to justify that choice to themselves or others over and over, Dell says.

New technology means that women can choose to become mothers well into their 30s and 40s. Duke’s Reproductive Endocrinology & Infertility Clinic offers in vitro fertilization, artificial insemination, and other state-of-the-art options for women who have problems getting pregnant or repeated miscarriages.

Many women are helped by such measures -- but not all. Through her book and private practice, Dell often counsels women with “baby lust” who do not become pregnant right away -- or find out they can never bear children.

Dell, who chose not to have children, writes in “Do I Want to Be a Mom?” that her career has always been her most cherished endeavor. While she is, in her own words, a nurturing person who loves puppies and children, she says she has never regretted her choice to not have children.

While Dell, now in her 50s, can’t relate personally to the angst of facing infertility, she does know how it feels when biology forces a woman to adjust her dreams. Several years ago, a progressive pain in her right hand forced her to give up her practice as an OB/GYN surgeon. She lost part of her identity. After a period of depression and much soul-searching, she retrained in psychiatry and made her way back to Duke, offering psychiatric treatments for reproductive-age women.

Along the way, Dell found a simple truth that surfaces in her book as advice for women in turmoil: “Things work out over time."

Says Dell: “As long as we have a sense of personal choice, we’re OK.”