The most common known cause of miscarriage is chromosomal abnormalities, i.e. abnormal chromosome number or structure in the fertilised egg. The likelihood of such anomalies increases significantly with age, which is why a woman's age is an important factor: as natural pregnancy rates fall, the risk of miscarriage increases from the age of 35. The following are also considered to be triggers for habitual miscarriage (repeated miscarriages):
A woman's menstrual cycle is controlled by hormones, and a hormonal imbalance can be the cause of recurrent miscarriages. Known hormonal disorders include PCO syndrome, hypothyroidism and progesterone disorders.
In women with coagulation disorders, problems with the blood flow to the placenta may occur during pregnancy. Due to the lack of supply to the baby, this condition can result in a miscarriage.
In rare cases, the mother's immune system reacts incorrectly to the fertilised egg, registering the embryo as a foreign body and rejecting it.
Muscle nodules in the uterus can affect the growth of the foetus and, in some women, can increase the risk of miscarriage.
Pregnancies that end before the foetus has reached a weight of 500 g are called miscarriages.
According to WHO guidelines, all pregnancies ending before the end of the 27th week of pregnancy are considered miscarriages.
About 80% of miscarriages occur before the end of the 12th week of pregnancy.
The risk of miscarriage is higher if the woman has already had a miscarriage and increases proportionally with the number of previous miscarriages.
For 20-25 year olds, the risk of miscarriage is on average 9%, while women over 45 have a risk of around 75%.