Women delay childbearing today for a number of reasons: pursuing education and careers, marrying later or not finding the right mate. Whatever the social reasons, women still face the same biological imperative. The 20s are the prime childbearing years when it’s much easier to get pregnant. Fertility begins to wane in the early 30s and to follow a fairly steep decline after age 35. A 35-year-old woman has a 50 percent chance of becoming pregnant over one year of unprotected intercourse. Between age 40 and 44, that rate drops to only 27 percent, and problems increase.
But modern reproductive technology has given women a way to try to slow the biological clock. For the past two decades in vitro fertilization (IVF) has become increasingly common and a relatively early option for the one in six couples who struggle with infertility.
IVF involves considerable discomfort and expense, and only a percentage of women have a successful outcome. A series of injections of female hormones stimulate the release of eggs, which are retrieved and then mixed with the partner’s sperm or donor sperm in the lab. If fertilization occurs, the embryos are implanted in the uterus. When multiple embryos are implanted to increase the chances of success there is a much greater risk of a multiple birth.
As women age they face a couple of serious physical challenges to pregnancy. As eggs become older there is a lower chance that a viable egg will be fertilized–increasing the risk of miscarriage and of Down syndrome, the leading cause of mental retardation. Older pregnant mothers also face a higher risk of developing diabetes, experiencing a spontaneous abortion, having an ectopic pregnancy, developing high blood pressure and of having a C-section.
Fertility clinics have options for women with aging eggs. Most clinics discourage women over age 43 from using their own eggs for in vitro fertilization even if they’re still menstruating regularly because the chances of a successful birth are so low.
Egg donation, which uses eggs harvested from younger women, has made it possible for many older women to carry and deliver infants. The technique using donor eggs is essentially the same as regular IVF except for the source of the eggs. After harvesting they are fertilized in a glass dish and implanted in the would-be mother.
Because retrieving eggs is not a simple procedure, the demand for donor eggs is high and some women wait for up to a year to receive a donation.
Donor eggs and hormone support have made it possible for women to push the historical boundaries of childbearing and motherhood. Women in their 50s have given birth to healthy babies, although they still have to solve the problem of how to reconcile the demands of parenting and an aging body.
The physical challenges of pregnancy and childbirth for older moms are at least partly offset by the fact that older mothers tend to be in good health, have more access to medical care and are highly committed to meeting the demands of parenthood. Many older parents are financially secure, have had an opportunity to fulfill career and other life goals and are now emotionally ready to invest in raising a child.
The trend toward women choosing to delay childbearing until their 30s, 40s and even 50s will likely continue as women establish careers and take advantage of their reproductive options. While assisted reproduction techniques are expensive and sometimes an uphill battle, it is an option for some. When it comes down to biology, the 20s and early 30s are the most fertile years when it’s easiest to conceive the old-fashioned way.
Michelle Herbert Thomas, PharmD, CDE—Rev. 5/19/2010 TNK
