Women's fertility declines as they age due to the decay of a protein that keeps the DNA in their eggs together like a 'rubber band', scientists say.
Figures show around one in eight pregnancies end in miscarriage, which becomes more common in the mid-thirties.
Now, fertility researchers are one step closer to understanding why after analysing the DNA of egg cells under the microscope.
They discovered the age-related decline of a protein called cohesin weakens vital structures of chromosomes in older eggs.
It is thought this causes an abnormal amount of chromosomes in the eggs - a main driver of infertility, alongside a decrease in their quality and quantity.
Too many or too few chromosomes may lead to failure of an embryo implanting. In cases where pregnancies do occur, the woman may miscarry later on.
Scientists found a lack of the 'rubber band' protein cohesin damages structures of the chromosomes, including the kinetochores. This could affect how the spindle fibres pull the chromosomes apart when the egg cells divide, causing an abnormal number of chromosomes
Co-author Martyn Blayney, of Cambridge's Bourn Hall fertility clinic, said: 'Recurrent miscarriage is one of the most heart-breaking experiences.
'We are committed to supporting research that will enable us to better understand the complex workings of the egg and help more people to achieve their dream of a family.'
The scientists, which included a team from the Max Planck Institute for Biophysical Chemistry in Germany, published their results in the journal Current Biology.
Women are born with all of the eggs they will ever have. As an egg cell develops, it divides and becomes 'mature'.
Each mature egg contains just one copy of each of the 23 chromosomes. A mature egg is released once a month, ready for fertilisation with a sperm.
During cell division, the chromosomes are pulled apart by spindle fibers to separate poles of the cell. The cell divides into two eggs between these poles.
Meiosis is a fundamental two-part biological process, which produces sex cells.
Although the end result (four cells with half the amount of normal chromosomes) is the same, the process varies significantly between males and females.
The process is more drawn out in women than men.
The first step, known as meiosis I, begins when the person is still a foetus.
This means that when a woman is born, all her egg cells stored in the ovaries are halfway through the saga of meiosis. They are sometimes referred to as immature egg cells.
The process resumes after puberty, but only for the eggs released during monthly ovulation.
Every month, when eggs are released, the genetic material within is pulled apart by in order to complete the complex process and, when