An old hypothesis that claims that as a woman ages, the eggs she will produce will have more faulty chromosomes - leading to miscarriages and developmental abnormalities - does not hold much water, says a new research.
The production-line hypothesis stated that the first eggs produced in a female's foetal stage tend to have better connections or "crossovers" between chromosomes.
But after counting the actual chromosome crossovers in thousands of eggs, researchers at Washington State University found that eggs produced later were no different from those produced early in the foetal stage.
"If the production-line hypothesis was true, you would expect lots of abnormal cells and you would expect them all to be happening late," said Ross Rowsey, one of the researchers.
"We do see a pretty high incidence of abnormal cells, but they are just as likely to be happening early as late," he added.
Rowsey studied more than 8,000 eggs from 191 second-trimester fetal ovaries. He saw a lot of variation within women and between women, but no relationship to a woman's age.
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"There have to be other factors involved," he said.
"The abnormal crossovers cannot be explaining all of it," Rowsey added.
The production-line hypothesis was put forth in 1968 by Alan Henderson and Robert Edwards, winner of the Nobel Prize for development of in-vitro fertilisation.