Word: eggs
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Dates: during 1990-1999
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...these issues pale before the newly revealed miracle of fertilization, an event so dizzyingly complex that researchers say the more they know, the more they wonder that it works as often as it does. The actual merger of egg and sperm turns out to be one of the most straightforward steps in the process -- and the easiest to duplicate in a test tube. The events that occur before and after that union, scientists say, are where the real troubles...
...limited supply of eggs is believed to be a chief reason that fertility decreases with age. Each month, starting at puberty, hundreds of eggs begin the maturation process. One of them, growing in a fluid-filled sac called the follicle, quickly establishes itself as the first among equals. In a normal cycle, only that single egg will be released to the Fallopian tubes for possible fertilization. About 1,000 more will wither away and disappear. So although a woman may have 400,000 eggs to start with, the number she can effectively use is closer...
...make matters worse for the aging female, the eggs that remain in her ovaries get older and less fertile with each passing year. Recent studies of egg donation provide strong evidence that it is the age of the eggs, and not the age of the reproductive system, that causes fertility to decline sharply after age 40: older women who receive eggs from younger women get pregnant at rates comparable to the age of the egg donor, not the age of the recipient...
...ranging from laser-beam surgery to inflating a tiny balloon within the clogged passage. Men with extremely low sperm counts can be helped toward fatherhood by artificial insemination, which puts what sperm they have directly into the cervix, or by microinjection, which puts a single sperm right into the egg. And for couples with sperm-allergy problems, a procedure known as sperm washing strips the sperm of some of the chemical antigens that trigger the allergic reaction...
Scientists attribute the implantation rates of GIFT to the way in which the fertilized embryo enters the uterus. In IVF the embryo is squirted, rather violently, into a reproductive tract that has been pretty roughly treated, first by various hormone treatments, then by the egg-retrieval procedure. In GIFT, by contrast, the embryo drifts quietly into the uterus, much as it would naturally. To further improve the success rates, Asch's researchers tried fertilizing the egg in a lab dish and then placing the pre-embryo, or zygote, directly into the Fallopian tube -- a procedure known as ZIFT (zygote intra...