The U-shaped fertility curve to protect women

A study published in Science has identified a safety mechanism, the U-shaped fertility curve , from adolescence to menopause, created by nature to protect women.

A mechanism that regulates that biological clock which ensures that a woman is fertile only for a small part of her life.

Among the authors of the important scientific work, we also find  Filippo Ubaldi  and  Laura Rienzi , respectively clinical director and laboratory director of the medically assisted procreation centers Genera .

In the study, 3000 oocytes of girls and women aged between 9 and 43 were examined.

Researchers have outlined some of the mechanisms that may affect women’s fertility. These mechanisms largely depend on natural chromosomal errors, errors which vary according to the age group.

“ We have known for a long time, ” explained Professor Eva Hoffmann from the department of cellular and molecular medicine at the University of Copenhagen, “ that we humans have a unique fertility curve compared to many other species. The curve begins slowly in the teen years and begins to decline again as women reach their 30s. And before this study we didn’t know what caused these changes .”

The fertility curve

Unlike men who don’t produce sperm until they hit puberty, women are born with as many egg cells as they will have throughout their lives. However, the oocytes are initially immature and do not fully develop until the start of the menstrual cycle.

When the oocytes are inactive, a kind of molecular glue makes the chromosomes stick together. Later, when the oocytes are maturing, the chromosomes divide. But the older women are, the greater the risk that this “glue” will break prematurely.

As a result, the genetic material is fragmented causing chromosomal errors which can, for example, lead to syndromes such as those of Down, Turner or Kleinfelter. Or lead to abnormalities that can make the oocytes unfertilizable or cause miscarriages.

Researchers found a  higher incidence of chromosomal errors during oocyte maturation also in adolescent girls : the oocytes did not reach a sufficient level of maturity.

During adolescence therefore, especially the larger chromosomes in the hereditary material, develop defects and therefore the probability increases that the oocytes cannot be fertilized or that the pregnancy ends in a spontaneous abortion.

During the transition from adolescence to being a young woman, it has been seen that the oocytes improve, and the chromosomal errors gradually disappear.

This improvement persists until the women are in their thirties, after which the oocytes have begun to show other types of chromosomal errors.

The grandmother hypothesis

Scientists still don’t know exactly why human fertility rises, peaks, and falls in a defined age range. By comparison, our fellow species, chimpanzees, do not experience menopause in the same way , but are instead consistently fertile throughout their adult lives.

According to Dr. Hoffmann, these could be two evolutionarily developed mechanisms in humans. First, a mechanism that protects very young women from pregnancy until their bodies are fully developed , and therefore able to better bear, and with less risk, childbirth.

Second, it could be a mechanism that potentially causes older women to take on a new supportive role, that of grandmother, when their children become able to have children of their own, a theory that some researchers call the “motherhood hypothesis” . grandmother “.

Abortions and infertility

Finally, Dr. Hoffmann points out that the new results could be used to improve the dissemination of information on the loss of a child in pregnancy, and improve the treatment of infertility in the long term.

Although abortions in pregnancy are still taboo, with this study we are now able to understand and demonstrate that it is a natural event.

At the same time, a greater understanding of the mechanisms underlying women’s biological clock should always be considered to plan reproductive life.

As we have often explained, PMA does not work miracles when the problem is the woman’s age, because it is not able to improve the quality of the gametes. 

It helps in many situations (tubal infertility, in case of male factor, in case of ovulatory problems, endometriosis, pcos,…) but when the problem is linked to the fact of being, by age, at the extremes of that inverted U curve , there is currently nothing that can improve the quality of female gametes. This research opens up new perspectives, but social interventions are probably needed so that couples can have the opportunity to look for a child when they are at the highest points of the curve.