Approximately 50% of miscarriages that happen during the first trimester are due to a chromosomal problem with the developing foetus. Usually there will be the wrong number of chromosomes – too many, or too few – which means the foetus is unable to survive. The risk of chromosomal abnormalities is higher in older women, which is one of the reasons why older mothers are more likely to experience miscarriages than younger women. In women over 45, the risk of miscarriage can be as high as 50%.
Other factors that can result in early pregnancy loss include improper implantation of the fertilised egg, issues with the development of the placenta, structural problems in the female reproductive system, chronic conditions (eg. diabetes, kidney disease, thyroid disease), and a problem with the male’s sperm.
Infections and severe food poisoning can both increase the risk of miscarriage. This is one reason why women are advised to consider their diet during pregnancy and avoid food types that are associated with a higher risk of food poisoning, such as unpasteurised dairy, undercooked meats, raw eggs, and raw shellfish. Pregnant women should also limit the amount of tuna and other large fish due to potential mercury content which may affect the healthy development of the child’s nervous system.