Researchers at the Washington State University have debunked a major hypothesis that states older woman have a higher number of miscarriages and children with birth defects because the eggs produced by them have weaker connections with chromosomes.
The team said that they did not find any evidence that validates the 46-year-old 'Production-Line Hypothesis' in their study.
Researchers arrived at the conclusion after comparing thousands of eggs that were produced during different ages. They counted the actual chromosome crossovers or connections and found no differences in the numbers of crossovers between eggs that were produced early on in life and eggs that were produced at a later stage.
"If the production-line hypothesis was true, you'd expect lots of abnormal cells and you would expect them all to be happening late," said Ross Rowsey, a doctoral candidate in WSU's Center for Reproductive Biology, in the press release. "We do see a pretty high incidence of abnormal cells, but they're just as likely to be happening early as late."
Researchers explained that instead of chromosome crossovers, faulty chromosomes seemed to impact the risk of miscarriages and developmental abnormalities. They said that analysis showed aneuploidy, which occurs when there is incorrect number of chromosomes, could be responsible for more than one-third of miscarriages and birth defects.
The team stated that older women tend to have aneuploidy more often than young women.
"The age of the woman is probably the most important risk factor associated with any human genetic disease," said co-author, Terry Hassold, a WSU professor of reproductive biology. "It's an extraordinary complication to human reproduction. By the time a woman is in her 40s, it's likely the majority of her eggs don't have the right number of chromosomes. And if you don't have the right number of chromosomes, you'll either have a miscarriage or a congenital disability."
The findings were published in the American Journal of Human Genetics.
