To date we have not found one particular cause for (recurrent) miscarriage. Probably various factors play a role, both in the embryo and the mother.Genetic factors Environmental factors Hormonal factors Anatomical abnormalities Viral infections and immunological causes
We know that a large number of human embryos show some sort of genetic abnormality. Particularly when the woman is older and the egg quality decreases, there is a higher risk of chromosomal abnormalities. This is why (recurrent) miscarriage is more frequent in an older population.
A couple can have a large proportion of abnormal embryos as a result of a genetic abnormality in the DNA. However, this diagnosis is not very frequent, only in two to five percent of the couples who had three miscarriages.
Some researchers believe that even in this situation embryonic genetics is not the true cause of the miscarriage. The problem lies in the lining of the womb, which is not selective enough. It should have the capacity to recognise abnormal embryos and not allow them to implant. If that went well, there would be no pregnancy and the embryo would follow the ‘normal’ path of the menstrual cycle.
The following ‘external’ factors can be related to (recurrent) miscarriage:
- heavy intake of caffeine
- exposure to anaesthetic gases, tetrachloroethylene (used in dry cleaners), isotretinoine (medication for acne) and other toxic substances.
No connection with other external factors can be shown. There are no studies illustrating the effects of bedrest, physical exertion, physical activity or e.g. fitness programmes.
Mild hormonal abnormalities have not been shown to lead to recurrent miscarriage. However, badly treated hormonal problems such as the following do increase the risk:
- (unregulated) diabetes;
- serious thyroid problems
- polycystic ovarian syndrome.
- prolactine level in the blood that is too high; and
- low progesterone levels in the period following the implantation of the embryo.
In the general population, two to four per cent of women are found to have an abnormality in the uterus: fibroids inside and outside the uterus, the presence of a division (septum) or adhesions (Asherman syndrome). This defect is present from birth, and means the embryo is unable to develop properly.
In 10-15% of women who have had recurrent miscarriage, an abnormality in the uterus is found, often a septum.
Viral infections and immunological causes
There is little hard evidence that infections can cause recurrent miscarriages. On the other hand, abnormalities in the immune system, although rare, can lead to recurrent miscarriage (see also scientific project).
In most cases, this is due to an excess in antibodies, against the body's own tissues and cells. This is known as an auto-immune condition. Recurrent miscarriage is often caused by the antiphospholipid syndrome.