Reproductive Technology

Age must be taken into account when couples are considering assisted reproductive technology. In humans, the age of the oocyte, not the age of the uterus, is the main cause of reproductive failure in IVF and embryo transfer techniques. Embryos formed from older oocytes demonstrate an increased incidence of aneuploidy. In some other species, such as in rabbits, an aging uterus can keep an embryo from being implanted. The use of cryopreservation to circumvent reproductive failure in humans, cattle, and horses has already been successfully employed and is likely to be developed further.

Sperm generated by older men are capable of successfully producing normal embryos. However, as sperm age, they are exponentially more likely to contain new gene mutations. Older oocytes, on the other hand, do not appear to be more likely to contain new mutations. Scientists are unsure exactly how age affects oocyte integrity. Oocyte maturation takes place only before birth in the female, so no new oocytes are produced during the entire reproductive life of the female. This is quite different from spermatogenesis, which can continue into old age. Thus, oocytes from older women may be forty or more years old when they are collected and used to form the embryos.

Oocytes must reach full maturity before they can be ovulated normally and before they can be fertilized, even artificially, to form embryos. If immature oocytes could be artificially forced to mature in vitro, follicles could be taken from the ovaries of dying or dead women, or from cancer patients planning on undergoing chemotherapy treatments, which can damage oocytes. Unlike immature oocytes, immature sperm can effectively be used in fertilization. Additional research is needed in this area of assisted reproductive technology.