As you get older, you know that your body is going through changes, but what exactly is happening to your eggs as you enter your 30s ... and beyond?

You only have 100-200 thousand eggs left

You are born with one to two million eggs in your ovaries. By the time you reach your 20s, you only have 100-200 thousand eggs left. Even though you have far fewer eggs at this time, your fertility is still at its prime.

While you continue to lose eggs each month throughout your 30s, you should have enough to create an embryo. It's in the later end of your 40s that you begin running out of eggs. Dr. Andrew K. Moore, MD, an infertility specialist says, "By age 50, most women have few if any eggs left, which is the primary reason for menopause."

Egg abnormalities are more common

Even though most pregnancies during a woman's 30s are healthy, the quality of her eggs decreases as she gets older. Moore explains that aging eggs sometimes have abnormal chromosome number. These chromosomes are the DNA which will be passed to your baby. So when an egg has too many or too few chromosomes it will create an abnormal embryo. An embryo with an abnormal amount of chromosomes will not implant, end in miscarriage or cause conditions like down syndrome.

Your chances of getting pregnant decrease

While you can certainly get pregnant in your 30s, your likelihood decreases. "The decade of the 30s sees a significant decrease in fertility," said Dr. Moore. "The chance of pregnancy per month at ages 20, 30, and 40 are, respectively, 40 percent, 25 percent, and 7 percent."

You can check your fertility

Beyond the statistics about your chances of getting pregnant at your age, there are ways to check your individual level of fertility. You can get a blood test and ultrasound to see if your ovaries are aging at a normal rate.

However, what does Dr. Moore suggest as the best indicator of fertility? "Simply trying to get pregnant."

You will probably still have a healthy pregnancy

If you're in your 30s, there's good news for you. Dr. Moore said, "Most pregnancies produced by women in their 30s will be completely healthy."

How to increase your fertility

"Depending on family size goals, probably the most important thing is to not unduly delay child bearing." However, since that's not always feasible, he recommends freezing your eggs if you are 30-35 and don't have any clear plans to start a family.

Beyond that, the best way to keep your body fertile is to take care of it. According to Dr. Moore, when it comes to maintaining a fertile body "healthy diet, healthy weight and moderate amounts of exercise are helpful."