Perimenopause, also called the menopausal transition, is the time when a woman's body makes a natural shift from more-or-less regular cycles of ovulation and menstruation toward menopause, said MayoClinic.com.
Discovery’s How Stuff Works website added that perimenopause may start for some in their 30s. For others, it comes in their 40s or even 50s.
Perimenopause can last anywhere from 2 to 10 years, reported Prevention.com. Women officially reach menopause when they've gone 12 months without a period.
As a woman goes through the menopausal transition, her body's production of estrogen and progesterone fluctuates, said Mayo Clinic. These hormonal changes are at the root of changes in the female body.
The hallmark of perimenopause is change in menstrual periods. Dr. Oz wrote that the time between periods -- the number of days a period lasts or how much one menstruates -- any or all of these can be altered.
During perimenopause, about 65 to 75 percent of women experience hot flashes. The intensity, duration and frequency vary, said Mayo Clinic.
Sleep disruption is another symptom. Prevention.com wrote that estrogen and progesterone help regulate sleep. When they're out of whack, so is sleep.
Some women experience mood swings, irritability or increased risk of depression during perimenopause, said Mayo Clinic, but the key may be sleep disruption caused by hot flashes.
Mood swings may also be caused by factors unrelated to perimenopausal hormonal changes.
Reduced estrogen may weaken bladder control causing urinary incontinence, said Discovery.
Mayo Clinic added that when estrogen levels diminish, vaginal tissues may lose lubrication and elasticity, making intercourse painful. Diminished estrogen levels may also leave women more vulnerable to vaginal infections.
These hormonal changes may also reduce a woman’s sex drive. However, studies show for many, a good sex drive before perimenopause will return postmenopause, said Prevention.com.
With declining estrogen levels, women start losing bone more quickly than they replace it, increasing the risk of osteoporosis, wrote Mayo Clinic.
Prevention.com cautioned that extra weight may settle in the mid-section when estrogen levels dip and testosterone increases. Plus the stress of hormonal fluctuations can cause the body to secrete more cortisol, high levels of which stimulate fat storage around the belly.
Declining estrogen levels may lead to unfavorable changes in women’s blood cholesterol levels, including an increase in low-density lipoprotein cholesterol (the "bad" cholesterol).
At the same time, high-density lipoprotein cholesterol (the "good" cholesterol) decreases in many women, wrote Mayo Clinic. Both increase the risk of heart disease.
Memory loss is another symptom. Prevention.com said that one study showed 60 percent of perimenopausal women experience short-term memory loss and have trouble concentrating. It seems to be temporary as after menopause women generally return to normal.