At least 15 to 20 percent of all pregnancies end in miscarriage. Biologists puzzling over what can go wrong when egg and sperm get together are now one step closer to solving the mystery.
Human eggs are more prone to errors than, say, those of mice or any other species that has been studied. Often these errors come from faulty chromosomes, which account for more than one-third of miscarriages and birth defects.
The risk goes up as a woman ages. The question, though, for reproductive biologists has been: Is it the age of the woman herself, or the age of her eggs?
Ross Rowsey, a Ph.D. candidate at Washington State University, says for nearly half a century, the eggs were considered suspect.
“So this hypothesis said the last eggs made would be the last eggs ovulated, and because if they were the last eggs made, they would be worse eggs, was the theory,” Rowsey said. “But our evidence suggests it’s not exactly that. You form bad eggs — it’s going to happen — but it’s just as likely to happen early as late.”
The new research doesn’t explain why older women have more miscarriages. But Terry Hassold, a WSU biology professor who co-authored the study, is optimistic.
“Now what we can think about doing is investigating stages at which the egg is vulnerable, and you can think, then, about trying to develop some sort of method that might provide, say, a protein that might be degrading with the age of the woman,” Hassold said.
Hassold says he’s particularly intrigued by what could be happening during the egg’s resting stage, when it’s waiting around — sometimes for up to 50 years — before ovulation.
