Fertility issues: Your natural increase in FSH may be so stimulating to the ovary that it brings more than one egg to maturity. That's why if you were to get pregnant in your late thirties, you're more likely to have multiple births! (This probability drops off in your forties, unless you use fertility drugs, which also promote multiple births.) And since birth defects increase in women over 35, you are advised to consider genetic counseling before conceiving.

Stage-specific advice: "The first sign of elevated FSH is a call to accelerate your childbearing plans, particularly if you wish to conceive without medical intervention in the future," says Dr. Metzger. To maintain your ovulation consistency, you may want to consider natural supplements such as vitex or, if you are currently trying to conceive, a prescription for clomiphene citrate (Clomid).

Early Perimenopausal Stage

Approximate age: 42 to 46

Hormone levels: Your FSH may have doubled from the last stage, up to around 30 mIU/mL. Estrogen could be declining (under 80 pg/mL) due to lower follicle quantity and quality, or it may be temporarily elevated (above 100 pg/mL) in an attempt to modulate high FSH.

Characteristics: As you get deeper into the menopausal transition, not only is the follicle releasing less estrogen, it's also skimping on progesterone, which normally soars in the second half of your cycle. With only moderate amounts of estrogen stimulating the uterus, and no progesterone, there's less uterine lining to shed, and you do so earlier in your cycle. Consequently, your cycles may shorten to 24 to 27 days instead of 28 to 31, and your periods might be heavier or lighter than they used to be.

Fertility issues: Pregnancy and labor may require more medical attention for women over 40. You are almost twice as likely to have a cesarean birth as younger women, have a 7 percent chance of developing gestational diabetes (compared to 1.7 percent for a woman in her twenties), and are more likely to experience high blood pressure in pregnancy (even if you didn't have it already). Hopefully, you've kept up with a fitness program and optimized your nutrition as part of your preconception care plan -- which can help you beat the odds for high-risk pregnancies, says Dr. Minkin.

Stage-specific advice: Whether or not you have opted to use medical intervention like fertility drugs or in vitro fertilization (IVF) to increase your chances of conception, make sure you ask your doctor about taking progesterone to help the uterine lining build up enough for a fertilized egg to implant and stick, urges Dr. Metzger.

Late Perimenopausal Stage

Approximate age: 46 to 50

Hormone levels: Your FSH levels continue to climb, typically as high as 50 mIU/mL.

Characteristics: Even if your very high FSH successfully stimulates a follicle to mature, that follicle can be "deaf" to the next signal down the line, which is LH and its cohort hormones telling it to release the egg. Expect ovulation to be hit or miss -- this stage is characterized by two or more skipped menstrual cycles. And then, just when you thought you could stop clipping tampon coupons, your period might come back. It may be a "phantom period" where you don't ovulate but still have some endometrium to shed, or you may resume your old ovulation pattern for a few more months or years. The less frequently you ovulate, the less estrogen you produce -- which often means more noticeable perimenopause symptoms.

Fertility issues: Mentally prepare yourself for pregnancy loss, since half of pregnancies to women over 45 end in miscarriage. "And since childbirth is more aerobic than a half marathon, it's essential that you are physically 'trained' before conceiving. At the least, try to walk 3 miles every other day," says Dr. Minkin.

Stage-specific advice: "When considering if you have what it takes to raise the child to adulthood, apply the hoop-shooting rule: Ask yourself if you will be energetic and fit enough to shoot hoops with your child on their 13th birthday," Dr. Minkin advises.

Menopause and Postmenopausal Stage

Approximate age: 50+

Hormone levels: Your FSH levels will reach their peak, between about 50 and 70 mIU/mL, where they will stay. Your ovaries significantly decrease their production of estrogen, although the adrenal glands continue to produce small amounts.

Characteristics: Once you haven't had a period for an entire year, you're officially in menopause. You can now be almost certain of not flip-flopping back into a surprise ovulatory cycle. Of interest, you may still have a few hundred or even a few thousand eggs in your follicles, but the last few hundred generally don't develop.

Fertility issues: Your last option for getting pregnant now may be the high-tech medical intervention of using a donor egg with an IVF treatment -- that is, if you have the financial capability and your doctors think you're likely to respond. When over-40 women undergo IVF with younger women's eggs, they actually have very similar conception rates as younger women. In order to truly "level the playing field," though, older women may need to have more embryos transferred than younger women would and take progesterone along with standard fertility drugs.

Stage-specific advice: The ASRM advises women to have counseling to understand the full legal, ethical, psychological, and social issues involved with using donor eggs or sperm. In fact, RESOLVE: The National Infertility Association recommends that both the couple receiving the egg and the donor of the egg work with a lawyer.