Doctor, can I still get pregnant?

October 7, 2011

A very common question of perimenopausal women is whether or not they are still able to get pregnant, and this inquiry may originate from one of two concerns. Some women in the perimenopausal range may still want to conceive, either to start a family or to add to an existing one, and are seeking information to help with that decision.

 

A very common question of perimenopausal women is whether or not they are still able to get pregnant, and this inquiry may originate from one of two concerns. Some women in the perimenopausal range may still want to conceive, either to start a family or to add to an existing one, and are seeking information to help with that decision. On the other hand, many sexually active women have no further interest in conceiving, and contraception must still be a consideration. The age of cessation of menses, or menopause, may vary from the mid-thirties to the late fifties. The perimenopausal period is defined as the several years preceding menopause when the symptoms first appear, and it likewise has great variation. The following discussion assumes that the average age to stop menses is 50-51 years old; with 45 to 50 years old being the perimenopausal time. But one must keep in mind every woman is different and there is a wide age range at which these changes may occur.

The perimenopausal woman seeking information regarding conception, or avoidance of it, needs to realize the significance and the implications of changes that have occurred in her body. A woman begins with a large numbers of eggs in her ovaries when she herself is still a fetus.

A woman's ovaries contain over six million eggs at about the halfway point in her development inside her own mother's uterus (four and one half months of gestation). These eggs begin to disintegrate, or atrophy, even while she is still a fetus, and by the time she is born there are only around one to two million eggs left in her ovaries. The eggs continue to atrophy and by the time she reaches puberty there are only around 300,000 left. Considering she will ovulate only around 400-500 eggs in her lifetime, certainly this is still an adequate amount. After the age of 35 this disintegration and atrophy of the eggs begins to accelerate, and by the time a woman stops her menses, essentially all her eggs are gone. But of more importance to the perimenopausal woman is the fact that a large portion of these eggs are not viable during these last few years. That is, the egg may be released, but it cannot be fertilized or it will end in a miscarriage because of chromosomal problems. Thus, a woman's fertility begins to decline significantly after the age of 35. Spontaneous and successful pregnancies after the age of 40 become less common, and after the age of 45 are rare (but not zero!).

The woman seeking natural conception at this age will find that the facts are fairly discouraging. While 80% of women between 40 and 45 can potentially conceive with different methods, this percentage falls off dramatically after the age of 45. The average woman notices that by this time her cycle is already less regular. This irregularity makes the prediction of the date of ovulation, if it occurs at all, much more difficult. In addition, the eggs are of much poorer quality, and often cannot even be fertilized even if released. Even if spontaneous conception does occur, there is a much higher rate of birth defects and miscarriages with these pregnancies. For instance, the rate of miscarriage doubles after the age of forty. These factors, along with a higher obstetrical complication rate in this age range, demand that a woman consider her options carefully if she wishes to conceive in this period of her life. On the other hand, many advances have been made in assisted reproduction in this age range, and with such techniques as donor eggs and hormonal manipulation of the uterus, the conception and miscarriage rate can be significantly improved. A woman and her partner are certainly the only ones who ultimately have the right to make and pursue this decision.

So how does a woman determine if she can still conceive? Many subtle hormonal changes are going on during this perimenopausal transition before she actually stops her menses. The fact (good or bad) is that she will probably continue to ovulate occasionally, even if sporadically. And while many of the eggs may be nonviable, she will probably continue to release some good ones. Unfortunately there is not an accurate way to tell which are the good ones and which are not. Thus the question: "When am I no longer ovulating?" In order to understand some of the hormonal measurements utilized for this determination it helps to understand some of the basic mechanisms of the reproductive system.

The ovaries produce most of the female hormones (estrogens and progesterones) and release the egg at the time of ovulation. The ovaries are controlled or stimulated by a gland in the brain called the pituitary gland. The pituitary gland produces follicle stimulating hormone, or FSH, which helps to stimulate the ovary and ovulation. The body can tell when the ovaries are slowing down or not doing their job, and then the pituitary tries harder to make the ovaries work and ovulate. It does this by increasing the production of FSH in an effort to stimulate the ovaries to work. If the pituitary gland then detects an increase of estrogen in the bloodstream, it will then stop or slow down its production of FSH. The FSH production varies during the cycle and is intimately involved with ovulation; if the ovary stops working, the pituitary gland begins to produce high levels of FSH trying to get the ovaries to work. This is a concept that many people find hard to understand, why one hormone (FSH) goes up while other hormones (estrogens) are going down. It is simply the pituitary gland trying to get the ovaries to work again, producing high levels of FSH at menopause when the ovaries stop producing adequate levels of estrogens.

By measuring these levels and knowing what levels are critical, one can then determine when the ovary is no longer ovulating. This is the basis for measuring FSH levels in the perimenopausal woman. When a woman wishes to conceive during this perimenopausal time, often the health care professional will obtain a FSH measurement to determine her chances of getting pregnant. A woman whose FSH levels have already started to increase has a significantly reduced chance of conceiving. The timing may also be important as to its level. For instance, if a woman is on birth control pills, the body will detect the estrogens in her body and lower the production of FSH, thinking the ovary is working fine. Thus, if a woman is on oral contraceptives or replacement hormones (estrogens), then she has to discontinue them for a period of time in order to obtain an accurate reading of the FSH. Most experts suggest a week off all hormones in order to determine the level, but some newer studies suggest it may take up to two weeks to get a reliable measurement.

If the FSH level is normal in a perimenopausal woman desiring conception, then she is over the first hurdle and can move on to other evaluations in an effort to conceive. But if a woman does not want to get pregnant, can she relax if her FSH level is elevated? Probably so, and many experts suggest relying totally on an elevated FSH level as an indication to discontinue using contraception. However, there are some researchers who suggest that it is also important to ensure that the woman is no longer having menses. It is rare, but occasionally the FSH level will oscillate somewhat during this time. Thus the FSH level may be elevated intermittently but the woman may still ovulate sporadically. In this situation a woman needs to also determine that she is no longer having menses to be absolutely sure she cannot conceive. Therefore, it takes a combination of an elevated FSH level and no menses in order to be absolutely certain she will not accidentally conceive. While the chances of conception late in this perimenopausal period are very, very low, they are probably not zero until she completely stops her menses and has an elevated FSH level of over 30 to 40 mIU/ml.