All women see a decline in their fertility beginning around age 35, making it far more difficult -- but not impossible -- to conceive naturally. Note, however, that the risk of birth defects, including Down syndrome, increases as a woman ages, as does the risk of an ectopic pregnancy, which can be life threatening.
Treatments such as in vitro fertilization have extended the window of fertility significantly, making it possible to conceive well into the mid-40s. For many doctors, however, the cutoff point is around age 45, a time when many believe a woman’s eggs are no longer healthy enough for a normal conception -- although normal pregnancies can and do occur at this age.
Moreover, with the inception of donor eggs -- those produced and provided by a younger, more fertile female -- a woman could actually carry a child and give birth well into her 60s and beyond, depending on her individual health status. Although this is possible, it is not necessarily a recommended or accepted practice.