Doctor: Ralph Kazer, M.D., is a professor of obstetrics and gynecology and chief of the division of reproductive endocrinology and infertility at the Feinberg School of Medicine at Northwestern University, in Chicago.

Psychologist: Linda Applegarth, Ed.D., is director of psychological services and associate professor of psychology at the Center for Reproductive Medicine at Weill Medical College of Cornell University, in New York City.

What's the textbook definition of secondary infertility?

DOC Infertility is generally defined as the inability to conceive after one year of unprotected intercourse. Secondary infertility refers to a patient who fulfills this definition but who has given birth at least once in the past.

How common is secondary infertility?

DOC About a quarter of the 1,500 patients my practice sees each year are experiencing it. But just when these patients make that judgment call depends on their ob-gyn: Some doctors are comfortable doing their own testing; others send us their patients right away. [Note: According to the National Infertility Association, more than 3 million Americans are affected by secondary infertility.]

What are the main causes?

DOC The list of causes of secondary infertility is the same as for primary. The testing is identical, too: We'll need to know that the man's sperm is plentiful, that the woman is ovulating, and that her tubes are open. And we'll do an ovarian-reserve assessment, which measures the impact of age on egg quality. The one fertility problem that always develops as women age is a decline in the quality of the eggs, and women with egg-quality problems who have turned to fertility drugs may at a certain point have to consider ceasing that course of action. That's the time to think about using donor eggs.

Although age-related concerns dominate, there are a few other possible causes. In order of decreasing frequency, they are fallopian-tube blockages, uterine fibroids, and uterine polyps. In addition, the man may have issues with semen quality. Tube blockages and sperm-quality issues can be very effectively dealt with using in-vitro fertilization (IVF), while uterine fibroids and polyps are benign disorders that are treatable both medically and surgically.

Can complications in a first pregnancy—either during gestation or delivery—compromise a second?

DOC Very rarely. If scar tissue develops in the uterine cavity after a delivery—if tissue is left behind, for example, or the mother develops an infection—it can cause problems. But scar tissue isn't a common cause of infertility, and it can sometimes be removed surgically anyway.

At what point should someone seek help from a specialist or therapist?

DOC In the absence of any explanation, such as blocked tubes or poor-quality semen, the usual guideline is to seek help after a year of well-timed, unprotected sex. But we recommend that women in their late 30s or early 40s come in after six months. For initial therapy, you should go either to a reproductive endocrinologist or to a GP or ob-gyn with experience doing fertility work-ups (confirmation of ovulation, semen-quality analysis, etc.). And if the clinic you've picked feels like a mill—like you're one of a thousand patients—keep shopping. If you live in a big city, you'll have more choices. Look for a program that's big enough to offer a full range of services, such as intra-uterine insemination and IVF, but not so big that you feel lost. In my region, the Midwest, the clinics attached to Northwestern University, the University of Iowa, and Washington University in St. Louis are good examples.

PSYCH People are very different. Some will sense right away that it's beneficial to have psychological support, but most women or couples don't speak to me until they've reached a crisis stage or they have to make difficult decisions, such as whether to adopt. That's more likely to be when they'll seek ways of coping more effectively. Working with a mental-health professional can help them avoid displacing a lot of hurt, anger, and disappointment onto others.

Is it normal for women with secondary infertility to feel resentful of mothers who have been able to conceive more than once?

PSYCH Completely. There's this sense that everybody except you has control over their lives, which leads to feelings of anger and resentment. To temper these feelings, get support, and seek out other couples who are going through the same thing.

Is secondary infertility as tough on couples as primary?

PSYCH The element of disbelief is just as common either way. While I feel they're equally brutal, there's an added dimension of shame among secondary patients for wanting another child so desperately—they've been blessed with one child already, and some might say that should be enough. People with primary, in particular, have a difficult time feeling any compassion for those with secondary. So secondary-infertility patients don't have as many outlets for talking about their feelings. There are those who will experience it as a loss, and for some it can feel like a death.

What's the best way to respond to comments like "You should feel lucky to have a child already" or "Why not just adopt?"

PSYCH People often inadvertently put guilt trips on couples going through secondary infertility, although their intent is probably to offer solace: "You have a wonderful child. What are you worrying about?" How you deal with these comments will depend on your personality. Some withdraw, which I don't think is effective. Others laugh it off and say, "We have such a great kid that we want another one." But in response, choose your words carefully. If you're in a casual conversation, it may not be useful to call someone on comments like this. On the other hand, it's important to give family and close friends feedback. As for the adoption question, one of the best responses is "We're considering a lot of options." It doesn't let people know they've been rude and also doesn't reveal where you are in your decision-making. A lot of people don't understand what the process of adoption is like, and how huge the emotional component is for most couples.

For friends of those experiencing secondary infertility, what's the most sensitive way to approach the subject?

PSYCH The best way to console is to say, "I just want you to know that I support you in any decision you make." Whatever you do, don't withhold information about your own fertility. It's very demeaning when people are pregnant and don't share it because they want to "protect" a person going through infertility. It makes the infertile person feel like a child.

Are there any helpful books or websites?

PSYCH I'd recommend A Few Good Eggs: Two Chicks Dish on Overcoming the Insanity of Infertility, by Julie Vargo and Maureen Regan, and Infertility Survival Handbook, by Elizabeth Swire-Falker. And I've found the website resolve.org helpful.