Thinking of having another child? You may have less time than you imagine to conceive without difficulty. Still, you may be able to take steps now to improve your chances.

To help judge the state of your fertility, consider these questions:

1. How old are you?

Age is by far the biggest factor in fertility, and even the most advanced infertility treatments aren't always able to turn back the clock. "Women are postponing childbearing until later in life - that's the very reason we see more problems today," says Pamela Madsen, executive director of the American Infertility Association.

Some researchers believe that fertility peaks as early as a woman's late 20s, and there's a consensus that by her early 30s, both the quantity and the quality of her eggs have begun to decline.

It's a gradual process, so there's certainly no need to panic. But if you're 30, you may not want to wait ten years to start trying to get pregnant again. At age 35 about three-quarters of women will be able to conceive without treatment, but by age 40 only half will, says Owen Davis, M.D., director of the IVF Program at Cornell Medical Center in New York City. By age 45 it's under 10 percent.

The risk of miscarriage also goes up with age. At 35, about one in five pregnancies doesn't result in a live birth; by age 42 more than half fail, according to a study of over 500,000 women million women in Denmark. An older egg becomes an embryo that's more prone to genetic damage, researchers believe.

Infertility is traditionally defined as the inability to conceive after one year of unprotected sex. "In my opinion, a woman under thirty-five should try to conceive for that amount of time before she seeks medical help to find out why she's not getting pregnant," says Magdy Milad, M.D., a reproductive endocrinologist and an associate professor of obstetrics/gynecology at Northwestern University Medical School, in Chicago. "Between the ages of thirty-five and thirty-nine, she should try for six months. And after the age of forty, she should try for three months and then see a doctor for an evaluation, just to make sure that nothing's wrong and she doesn't run out of time to try treatment."

2. Do you smoke?

If so, you're hurting your chances of getting pregnant at any age. Exposing your eggs to nicotine will not only affect the quality of your eggs but decrease your ovaries' supply. The more cigarettes a woman smokes daily, the lower her chances of conceiving. Smoking can also speed up the age at which menopause begins, prematurely closing your lifetime window of fertility.

The good news is that quitting now can restore much of your fertility. It's not immediate, though. "Once a woman quits, it can take several months for smoking-related toxins to be cleared from the body," says Dr. Milad.

Passive smoking interferes too: In one study, women exposed to smoke at work or at home were less likely to conceive within a year than peers who were exposed to little or none.

3. Are you at a healthy weight?

Being seriously over- or underweight - for a woman who's 5 foot 4, for instance, being heavier than 175 pounds (a body mass index of 30) or lighter than 105 pounds (a body mass index of 18) - may have a bearing on fertility, but only if it affects ovulation.

If your periods are normal, your weight is unlikely to impact your ability to get pregnant, says Bryan Cowan, M.D., chairman of the department of obstetrics and gynecology at the University of Mississippi Medical Center, in Jackson. But if you're overweight and your periods are irregular, talk to your doctor. On the other hand, if you're very thin or have recently lost a lot of weight and your periods have become irregular or have stopped, gaining weight may be the first step toward fertility.

4. What medications or remedies are you taking?

Thousands of prescription and over-the-counter medications - as well as herbal remedies - can have an effect on fertility. But the main concern is a class of drugs that affect your body's production of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) - key players in your ovulatory cycle. These include steroids (for asthma and rheumatoid arthritis), as well as prescription medicines that contain metoclopramide (for gastrointestinal upset) or phenothiazines (for anxiety.) It's always a good idea to talk with your doctor about which medications you are taking - or have taken - that might have an impact on fertility.

Contraceptives may also have an effect. If you've been on the Pill for a long time, it may take two to five months for your body to start ovulating normally once you go off it; that's also true for the newer hormone-based contraceptives like the Mirena IUD or the Nuva ring. "It's a myth that taking the Pill will prevent you from getting pregnant in the future," says Helane Rosenberg, Ph.D., egg donor coordinator at IVF New Jersey, in Somerset "But if you've been taking it for a long time, it could be masking a problem that would make you ovulate irregularly if you weren't taking the contraceptive."

The exception is if you've been treated with Depo Provera - in that case, the wait could be much longer. "Since the drug is injected into muscle, the hormone absorption may be so slow that it could take as long as a year for your fertility to return to normal," says William Gibbons, M.D., chairman of the department of obstetrics/gynecology at Eastern Virginia Medical School, in Norfolk. Norplant, though, has no adverse effect on fertility once it's removed.

If you're using herbal remedies, be wary: They're not regulated, so there's no requirement that their effects on conception and pregnancy be properly researched. Some reports have suggested that popular supplements - Saint-John's-wort, ginkgo, Echinacea - may negatively affect fertility, but other studies have found no effect, so there's no way to tell yet. "If you're having trouble conceiving and you're taking herbal supplements, you might want to stop, just in case," says registered dietitian Paul Thomas, editor of The Dietary Supplement, a newsletter for health professionals and consumers.

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