Throughout life, a woman’s fertility curve goes up and down, and researchers have now shown why. The results might have impact on fertility counseling and in the longer term for treatment of infertility.
Researchers have mapped out some of the mechanisms that may affect women’s fertility from the teenage years to menopause. These mechanisms largely depend on naturally occurring chromosome errors, errors that vary depending on age group.
This is the conclusion by an international research group in a new study, led by researchers from the University of Copenhagen. “We have known for a long time that we humans have a unique fertility curve compared to many other species,” says Head of Research and Professor Eva Hoffmann from the Department of Cellular and Molecular Medicine at the University of Copenhagen. “The curve starts out very poorly in the teenage years and starts to go downhill again when women reach their 30s. But until now, we have not known what is actually causing these changes.”
Unlike men, who do not form sperm until they reach puberty, women are born with all the egg cells they will have available throughout life. However, the eggs are immature and do not fully develop until the menstrual cycle begins. “While the eggs lie dormant, a kind of molecular glue will make the chromosomes stick together. Later, when the eggs are maturing, the chromosomes divide. But the older the women become, the greater the risk that the glue will break down prematurely,” says Hoffmann.
The hereditary material thus falls apart, resulting in chromosome errors which may, for example, lead to syndromes such as Down, Turner or Kleinfelter. Or which may make the eggs infertile.
In teenage girls, the researchers found a greater incidence of chromosome errors during the maturing of the eggs. This meant that in adolescence, the larger chromosomes in the hereditary material developed defects, and thus increased the likelihood that the eggs would be expelled by the body without being fertilized.
Scientists do not yet know for sure exactly why human fertility rises, peaks and falls within a defined age range. By comparison, our close fellow species, the chimpanzees, do not in the same way experience menopause, but are rather consistently fertile throughout their adult life.