Study Targets Causes of Birth Defects | WPN World People News

New research rules out a leading theory on why older women are at greater risk for having a miscarriage or a child with birth defects.

For almost five decades, it's been widely believed that the first eggs produced in a female's fetal stage have better connections between chromosomes. These connections are known as chromosome crossovers. This idea is known as the "Production-Line Hypothesis."

However, scientists at Washington State University (WSU) found that eggs produced early in the fetal stage are no different from those produced later.

"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 expert. "We do see a pretty high incidence of abnormal cells, but they're just as likely to be happening early as late."

Humans are born with 23 pairs of chromosomes -- one set from mom and one from dad. Each chromosome carries specific genetic material that defines who you are, such as whether or not you're male or female.

The production-line hypothesis was developed in 1968. Since then it has become one of the most commonly used explanations for why babies are born with the incorrect number of chromosomes -- an abnormality known as aneuploidy, the study said.

"The age of the woman is probably the most important risk factor associated with any human genetic disease," said expert. "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."

Another longstanding theory is that as women get older, their eggs have more abnormal chromosomes, which result in miscarriages and birth defects.

To further investigate these ideas, the study's authors analyzed more than 8,000 eggs taken from the ovaries of almost 200 second-trimester fetuses from elective abortions.

The eggs were treated so that the proteins at chromosome connections or crossovers would become florescent. This allowed the researchers to count and examine them.

Although there was variation among the women, the study revealed there was no link to their age.

The researchers concluded there are three stages at which problems could occur: when the chromosome connections are formed, during the long wait before ovulation when proteins must remain intact for years, and during ovulation and fertilization.

Source: HealthDay News