The majority of miscarriages occur due to the embryo having an unusual number of chromosomes, an event that is particularly common in women over 40 years old. New research from the Monash Biomedicine Discovery Institute (BDI) and University College London may illustrate why.
Led by Professor John Carroll at Monash University, the study analysed two processes of cell division – known as meiosis I and meiosis II – that occur in the final stages of egg development. During these two phases, the number of chromosomes in a fertilised egg is regulated by a protein called securin.
Because a woman has a finite number of eggs, formed when she was in her mother’s womb, her eggs age as she does. The findings, published in Nature Communications, suggest older eggs are less likely to have adequate stores of securin, interrupting the cell division process meiosis II.
Different numbers of chromosomes can result in Down’s syndrome or miscarriage. Women over 40 have a 50% chance of miscarriage, more than 3 times that of a woman in her 20s.
While this is only part of the story, Professor Carroll says the finding could go a long way towards promoting healthy pregnancies in women over 40, if securin levels can be regulated.
“Now that we have an idea of at least one of the causes of the increased incidence of chromosomal abnormalities and miscarriages in older women, we can attempt to find ways to prevent this happening.”