Fertility and age (Pregnancy)
If you’re in your 30s or 40s, you may be wondering whether you’ll have trouble getting pregnant. Fertility does decline with age. A woman is at her peak fertility between ages 20 and 24. If you’re in your early to mid-30s, you’re probably about 15 percent to 20 percent less fertile than you were in your early 20s. If you’re in your mid- to late 30s, you may be 25 percent to 50 percent less fertile than you were at your peak. If you’re in your early to mid-40s, your decline in fertility may be as much as 95 percent.
Here’s another way of thinking about it: In the United States, about 10 percent of women in their 20s report some difficulty getting pregnant. This percentage increases to 25 percent among women in their 30s and to more than 50 percent among women age 40 and older.
Studies suggest that your fertility declines slowly through your mid- to late 20s and early 30s. It then drops off more steeply once you reach age 35. Statistics bear this out: About one-third of couples in which the woman is over 35 have trouble conceiving a child. However, some research suggests that while this age-related drop in fertility decreases your chances of becoming pregnant in a given month, it doesn’t reduce your overall chances of conceiving. In other words, if you’re in your mid- to late 30s, getting pregnant may just take a bit longer than it would have earlier in your life.
Why does fertility decline as you get older? Researchers think it mainly has to do with the quality and quantity of your eggs. The receptiveness of your uterus and age-related hormonal changes also may play a role.
When you’re born, your ovaries contain all the eggs you’re ever going to have — about 2 million — although they’re in an undeveloped form. As you mature, most of the undeveloped eggs disappear, leaving only about 40,000 by puberty. During your reproductive life — about 30 years for most women — only about 400 of these eggs will develop fully, typically about one a month. When you’ve used up all your eggs and your ovaries no longer produce enough estrogen to properly stimulate the lining of your uterus and vagina, you’ve reached menopause.
Studies suggest that as you reach your mid-30s and your eggs get older, they decline in quality. They don’t look any different from younger eggs, and their advanced age doesn’t seem to make them less likely to be successfully fertilized by your partner’s sperm. However, some research suggests that when fertilization occurs, an older egg is less likely than a younger one to develop into a blastocyst — the ball of cells that becomes implanted into the uterus, causing pregnancy.
One possible reason for this is that older eggs are more likely than younger ones to have chromosome problems — both abnormalities and more mild degenerative changes. When conception occurs, these problems may prevent the fertilized egg from implanting and developing normally inside your uterus or they may even result in early miscarriage. The group of chromosomal abnormalities called aneuploidy is the most common cause of miscarriage early in pregnancy. In fact, aneuploidy often causes a miscarriage even before a woman knows she’s pregnant.
Scientists think that some women may use up their eggs more quickly than others, thereby reducing their chances of conceiving. When the pool of available eggs drops below a certain minimum level, fertility may be compromised. Women typically start losing more eggs per menstrual cycle around ages 35 to 40, when fertility also begins declining more rapidly. Doctors and scientists hope to someday develop therapies to slow accelerated egg loss, thus prolonging women’s reproductive lives.
Some studies have found that women in their mid- to late 30s tend to have a decline in uterine receptivity, which can prevent an embryo from implanting properly. However, other studies have found just the opposite, showing no evidence of decreased receptiveness with increasing age.
Changing hormone levels
As you reach your mid-30s, your body produces more follicle-stimulating hormone (FSH) and estradiol and less of a hormone called inhibin B. Scientists think these changes may indirectly compromise the formation of follicles — tiny sacs that each contain a single, immature egg — in your ovaries and the growing and thickening of your uterine lining in preparation for pregnancy, as well as the development of the growing embryo. More research is needed.
Tests to detect these hormonal changes have been shown to be valid predictors of whether you’ll be able to get pregnant through the use of assisted reproductive technologies, such as in vitro fertilization (IVF). But they’ve never been studied outside this context, so they may not be useful for gauging whether you’ll be able to get pregnant the “old-fashioned” way.
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Posted in Pregnancy