Word: egges
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...what if it doesn't work? What if egg meets sperm and nothing happens? Human sexual reproduction, as couples even before Sarah and Abraham have known, can be a heartbreakingly unreliable process. Even under the best of circumstances -- a fertile couple having intercourse at the optimum moment in the woman's cycle -- it fails 3 times out of 4. When conditions are less than ideal -- when the woman is over 35, for example, or the man's sperm is defective or in short supply -- the odds lengthen dramatically...
...remarkable advances, scientists have opened a new window on the mysteries of fertilization that shows for the first time not only how the process works but also what can be done when it doesn't. Doctors today can manipulate virtually every aspect of the reproductive cycle, from artificially ripening eggs in the ovary to inserting individual sperm directly into the egg's inner membrane. Now researchers at several U.S. clinics are pushing the scientific envelope even further, screening embryos for genetic defects in the lab before placing them in their mothers' wombs...
...techniques have also given birth to once unimaginable ethical dilemmas. Do sperm and egg donors have a claim on their biological offspring, and vice versa? Do embryos, frozen or thawed, have a constitutional right to life? How much manipulation of genetic material will society be willing to permit? "Technology makes us look at our most cherished conceptions of who we are and what we want to be," says Dr. Kenneth Ryan, a professor of reproductive biology at Harvard Medical School. "People have to decide what kind of society they want to live...
...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...