Your marriage is humming along, your work life is under control and now you want a baby, or possibly a second or third child. But you're over 35. What are odds of conceiving?

There's no one answer to that question because women differ biologically, says Miriam Greene, M.D., assistant professor of obstetrics and gynecology at the New York University Medical Center in New York City. " Generally, when you reach the age of forty-two, your chances of conceiving are ten percent, " she says.

That's because women in their 40s and late 30s enter perimenopause, the stage that precedes menopause during which your eggs start to age and estrogen levels (the hormone that helps creates the eggs) begin to decline. Symptoms include irregular periods (earlier than the normal 28 days apart); periods that are heavier than usual; and periods that involve spotting rather than a regular flow. Hot flashes may also occur during this stage.

But that doesn't mean you should be discouraged about being able to get pregnant, says Dr. Greene: "Unless you're in menopause -- meaning you haven't had a period for an entire year and blood tests confirm a lack of estrogen -- there are measures you can take to make it easier for you to conceive."

If you want a baby and have the symptoms of perimenopause, or are over the age of 40 and have been trying to get pregnant for three months without success, you should visit your gynecologist. Your doctor should review your menstrual cycle pattern over the past several months, get your complete medical history and give you a thorough physical exam to get a number of tests. One of these is the FSH (follicle-stimulating hormone) test. FSH is a hormone that signals your body to create eggs.

Your doctor should also test your estrogen and progesterone levels. It's best to have all these tests in the second or third day of your menstrual cycle because the results are more accurate at this time. You'll also want to test for metabolic disorders -- such as diabetes and hypothyroidism -- which can hamper your ability to get pregnant. If the hormone tests show you're not in menopause and everything else looks normal, your husband's sperm count should be checked.

If his sperm count is normal and test show that you're not yet in menopause, you can be given hormone injections that will increase your chances of getting pregnant, says Dr. Greene. If you do get pregnant, you may be given hormones to prevent a miscarriage during the first trimester, the time in which you're most vulnerable to miscarrying.

If the above measures don't work, you may consider visiting a fertility clinic that provides donor eggs and have a donor egg implanted in your uterus (a procedure called in vitro fertilization).

Rachel Fulton writes frequently on women's health issues. He work has appeared in several national women's magazines, including Redbook and First for Women.